One of the fundamental things that defines humanity is our sense of self-identity - an awareness of one’s self as an independent, thinking being shaped by its memories, its form and its environmental conditioning. Stories in which that sense of self is challenged by an identity theft that goes beyond simple bureaucracy and often involves complete substitution have been common in fiction, with examples including classics such as The Man in the Iron Mask (Dumas, 1850) and The Prisoner of Zenda (Hope, 1894). However science fiction offers the scope for far more unusually - and often morally challenging - examples of the ultimate identity theft.

Note: This is a big topic touching on several subtopics that could each have a whole entry to themselves, so I’m going to skim across a range of categories rather than do a deep dive into any one here.

Masters of Disguise

Physical appearance is perhaps the simplest property of an individual’s identity to duplicate. If no human contact or interaction is required, such a duplication might be sufficient to steal another’s identity. Naturally, many examples of such simple substitution in science fiction owe most directly to the Ruritanian fiction of Anthony Hope. These fall into two categories.

At its most basic, and perhaps most feasible, narratives abound of finding natural doppelgangers [1] - those with a close physical resemblance to the principal, or perhaps a likeness that can be refined through plastic surgery.

Examples of this abounded through the 1960s, particularly as plastic surgery became more advanced, and it was a staple of the SF-adjacent television genre of spy-fi, with examples to be found in The Avengers, The Persuaders, The Champions and many others. Often in these cases, the resemblances achieved and the speed and invisibility of healing verged on science fictional, and the motive was often to be found in either gaining military control or providing a means of escape for criminals (including Nazi war criminals). An example can be found, for instance, in The New Avengers episode “Faces” (1976), in which both the protagonist characters Mike Gambit and Purdey infiltrate a gang by pretending to be natural doppelgangers for themselves. The resulting confusion of identity has a poignant note when each believes the other to have been killed and substituted.

However science fiction takes the idea of natural (or slightly manipulated) doppelgangers to a whole new level with a range of masters of disguise who use physical tools or masks to steal the identities of others. These range from external technologies such as the artificial environment (AE) suits of The Tomorrow People (TV, 1973) or the shimmer field in Doctor Who (TV, Christmas special “The End of Time”, 2009), to latex masks as in Voyage to the Bottom of the Sea’s “The Man of Many Faces” (TV, 1967) or as used by the Hood in Thunderbirds (TV, 1965-66)

 While there is overlap here with the substitution techniques of the spy-fi drama serials, here the science fictional element is not simply in new medical techniques but rather in the technology required to make and wear sufficiently convincing masks and voice modifiers - these still lie well beyond our capabilities now.

Subtler Substitutes

Veering further into science fiction, a challenge to self-identity is found in individuals who can imitate the appearance, voice and other characteristics of a principal without any artificial aids whatsoever - shapeshifters. In a science fictional context these are usually aliens who can shift between physical forms near-instantaneously, providing a precise physical copy and supplementing it with mannerisms gleaned from a study of the principal.

Shapeshifting aliens abound in television science fiction in particular, with examples including the alien in Voyage to the Bottom of the Sea episode “Day of Evil” (1966) who appears variously as Crane and Nelson at different points; the cactus-like plant-person in Doctor Who’s “Meglos” (TV serial, 1980), the salt vampire in Star Trek episode “The Man Trap” (TV episode, 1966) and the Master of Infinite Disguise, Moid, in Terrahawks (TV, 1983). In each case the alien’s abilities are essentially left unexplained and indeed lie beyond scientific explanation, to the extent that the shape changes themselves veer towards fantasy.

Perhaps more feasible (if still reliant on Clarke’s Law science) are the Zygons of Doctor Who (first introduced in serial “Terror of the Zygons”, 1975) who can shape-change, but only if the principal remains connected to an organic device that scans both physical and mental characteristics, allowing them to be duplicated. Doctor Who and other fictions also propose many aliens whose imitations of individuals rely on projecting an image into the mind of the subject to be fooled, rather than changing physical form. In the latter case, the image of both shape, voice and personality could presumably drawn from the memory of the subject rather than entirely produced by the shape-shifter.

Perhaps in the grey area between natural shapeshifters and those using technical aides to act as substitutes, are another class of individuals in science fiction: android duplicates. These are mechanical and electronic constructs whose external appearance and mannerisms are designed to reproduce those of a specific human. The android in question cannot shift shape or change masks, but is designed to fool those around them into believing they are speaking to the principal. Such androids are usually designed with little to no self-awareness or independent thought and often make little effort to reproduce natural human interactions. Compared to disguises or shapeshifting, they have the advantage of being capable of storing extensive information about their principals, and of not having to unlearn a set of behaviours before adopting the imitation. The Stepford Wives (film, 1975; based on the 1972 book by Ira Levin), for example, makes their subordinate status explicit and desirable. In this story the independent-minded and insufficiently subordinate wives of the men in the Stepford country club are replaced by submissive robot replicas to the satisfaction of their men folk. No concealment of their true nature is necessary in this case. However other examples exist in which the robot replicas have to carry out a substitution over an extended time period - as in the Voyage to the Bottom of the Sea episode “The Cyborg” - or may even be unaware themselves that they are a duplicate. 

An interesting use case of android replication used to substitute for living creatures is in examples where deceased loved ones are reproduced. This is the case, for example, in Ray Bradbury’s Dwellers in Silence (short story, first appeared in Planet Stories, spring 1949; dramatised in the radio anthology series Dimension X in 1951 and X-Minus-One in 1955). Here a lone survivor left behind for decades in a city on Mars retains his sanity by producing android replicas of his dead wife and children. These robots are sufficiently convincing to not be recognised as such on first meeting by those in the first rocket to return after a long post-war absence, and indeed there is some discussion of the ethics of leaving them active versus destroying them when their inventor himself dies. While created as replicas, they are themselves now individuals.

Another Ray Bradbury story, published within a month of Dwellers in Silence, takes a more comedic approach to the issue. In Marionettes Inc (short story, first published in Startling Stories, March 1949; also dramatised for Dimension X and X-Minus-One), a man called Braling has a marionette (a robot replica) of himself made to substitute for him in keeping his over-demanding wife entertained while he entertains himself in other ways.

“It may be splitting hairs, but I think it highly ethical. After all, what my wife wants most of all is me. This Marionette is me to the hairiest detail. I’ve been home all evening. I shall be home with her for the next month. In the meantime another gentleman will be in Rio after ten years of waiting. When I return from Rio, Braling Two here will go back in his box.”

To his surprise, he finds the replica is far from keen to return to storage when not required. As the marionette explains, the technology is brand new, and has been deployed without being understood - the marionettes can think for themselves. It is perhaps a measure of justice that by the end of the story it is Braling himself who ends up in the box.

Pod People

A step beyond robot replicas are the fictions of organic replication: cloning [2].

Invasion of the Body Snatchers was a 1956 film, based on a 1955 novel by Jack Finney. Rooted in Cold War paranoia, this describes a rural American town in which individuals appear to change their personalities, leaving the protagonists struggling to understand what’s happening. It eventually becomes clear that the population of the town is being replaced by organic replacements grown in pods - essentially clones of the original. These pod people are clearly serving alternate aims to their principals and have a low affect (i.e. present the originals for the blank, unemotional exterior so notoriously associated with substitutions or brainwashing in science fiction). Their attempt to simulate the identities of their principals is shallow and only extends as far as necessary to secure the alien foothold (properties shared by the similar infiltrators created by “retrometabolism” from the recently deceased in Captain Scarlet and the Mysterons, TV 1967).

More explicit cloning (i.e. replication from the DNA and organic samples of the original) is a common trope in science fiction. In many cases, as in John Varley’s Eight Worlds series (short stories and novels, 1974-1998), cloning is developed as a medical tool. Bodies are cloned from cell tissue and matured with little or no independent brain activity. This blank slate permits the regularly backed-up, recorded memories and personalities of people to be downloaded into them, either as a precaution against accidental death or to enable a change of physical sex and gender appearance when desired. However the dangers of this system are explored in Varley’s short story The Phantom of Kansas (Galaxy magazine, Feb 1976). The protagonist of this story wakes a new body, and is told that they have been revived after a recent death. However it gradually becomes apparent that other things have been happening in the background - one result of which is the existence of a highly illegal clone-twin which has also had the memories and personality downloaded into it from an earlier recording, and which has endured a very different few months of life experience before the finale: 

“But he was me. It was all I had to go on. He was a me who had lived a very different life, becoming much tougher and wilier with every day, diverging by the hour from what I knew as my personality and capabilities. So I tried and I tried to think of myself doing what he was doing now for the purpose of murder. I failed utterly.
And if I could sink that low, I’d rather not live.” 

As far as each individual is concerned, they are the complete and original principal, leading to a moral and ethical dilemma regarding identity and self, as well as the right (or otherwise) of the clone to exist.

Questions regarding cloning were also explored by Lois McMaster Bujold in her Vorkosigan Saga novels Brothers in Arms (1989) and Mirror Dance (1994). Brothers in Arms introduces a clone of the original Miles Vorkosigan, created by an insurrectionist political conspiracy to replace him, infiltrate and destroy his family and (due to their powerful positions) the society structure on his planet. Unlike in Varley’s novels, clones in Bujold’s universe have fully developed brains, and develop their own personalities and characters based on their experiences. They are decanted as infants and forced-grown to physical adulthood in the space of about ten years (as opposed to decanted fully grown). On some planets they are fully recognised as humans, while on others they are not. Protagonist Miles is quick to recognise the independent identity of his clone, and to give him the name Mark, and ultimately the plan fails due both to the incomplete information available to Mark’s creators and the cunning of Miles himself.

In the sequel novel Mirror Dance, Mark Vorkosigan returns to his origin on the corporate, capitalist world of Jackson’s Whole, which routinely (albeit at great expenses) allows the production of clones for the wealthy. At the desired stage, the brains of these fit and healthy clones, who have typically been raised for about a decade, are removed and replaced in a risky transplant operation by the principals, who then live on in the youthful bodies. The brain, personality and identity of the clone is discarded as waste - a process shown throughout as abhorrent to all those except the perpetrators and those who profit from them. As a clone himself, and having been raised amongst others, Mark is eager to see the practice discontinued.

Turning to a more amusing, although also morally troubling, example, The Hitchhiker’s Guide to the Galaxy (Douglas Adams for BBC Radio, 1978) introduced the concept of a cloning machine which always got half-way through the construction of the next clone of a girl named Lintilla before the last was complete and so could never be turned off without committing murder. In this case it’s unclear whether the Lintilla clones (created as adults) shared memories as well as physical and general personality and it’s possible that these were closer to matter-duplication technology than traditional cloning.

Characterful copies

Of course, science fiction permits extrapolation into technologies still more distant and challenging than human cloning. On occasion these venture beyond a simple physical reproduction of an individual to instead duplicate them entirely, complete with memories and personality.

A classic trope of science fiction is the presence of parallel universes (and sometimes twin planets) in which individual persons are duplicated, often with subtle differences. Examples here include, for instance the film Doppelganger (aka Journey to the Far Side of the Sun, 1969) and the science fiction sitcom Red Dwarf (e.g. episode “Parallel Universe”, 1988). In each case, the protagonist finds themselves interacting with a world (and occasionally even an alternate self) which varies in significant ways from the familiar, often as a result of alternate decisions made or alternate cultural directions shaping their personality.

Perhaps the most famous, and most developed, of such alternates in science fiction television is the Mirror Universe of Star Trek. First introduced in the original series episode “Mirror, Mirror” (1967), it has been visited by each subsequent generation of Star Trek serials, including Deep Space Nine (e.g. episode “Crossover”, 1994) and, prominently, Star Trek Discovery (TV series, 2017-2024), in which it motivated a major series arc. Importantly, it is not usually possible for individuals from the mirror universe to imitate their prime principals, due to the radically different expectations and cultural backgrounds leading the mirror characters to be more prone to anger and outrage and less flexible at accepting perceived insults in the mirror universe - although substitution, of course, it does occasionally happen, as does the reverse masquerade. Importantly, these examples tend towards challenging protagonists to face what aspects of their own personalities may be suppressed by their cultural conditioning but still form part of their psyche.

While mirror universes typically provide cracked reflections, the Star Trek universe has also explored another form of duplication - and one which presents still larger ethical questions. The matter transporters of Star Trek work by dissociating the molecules of an individual at the point of despatch, transmitting the information associated through space and reconstructing the physical form at the point of arrival. Setting aside all the technical problems associated with the Heisenberg uncertainty principle, and the philosophical problems associated with the existence (or otherwise) of a soul, multiple variants of the television series have confronted an all-too-plausible scenario. The original series episode “The Enemy Within” (1966) introduced the idea of a transporter clone - an accidental second construct based on the same information by a failed or disrupted transport. This premise was revisited in examples such as Star Trek: The Next Generation (episode “Second Chances”, 1993) and Star Trek: Lower Decks (episode “Kayshon, His Eyes Open”, 2021).

In each case inert material has been used to create an individual with an identical physical body, identical memory patterns, and identical personality to the principal. In some cases it’s far from clear which was the first generated and which was the second, and in either case, it’s unclear whether chronological order of creation denotes priority since each are made from raw matter and the same information. After all, both the original and the clone legitimately believe themselves to be the original, both have an equal claim to the memories, friendships, belongings and careers which both remember working and training for. In the later Star Trek series, the preferred solution tended to involve renaming one of the two copies, and finding them an alternate career, although - since this robbed them of the family, friends and life they remembered - it’s unclear whether this is any kinder than the deconstruction which was the initial solution.

While Star Trek took the lead in this discussion, the general premise has also appeared elsewhere. The television series Farscape (1999-2003) featured an arc plot extended over the length of its third series, in which the protagonist John Crichton was ‘twinned’ creating two equal beings, neither of whom could be described as the original or a copy, and both of whom firmly believed themselves to be the true Crichton. In the end the two became separated, each accompanied by part of their original crew to lead separate adventures, and - perhaps inevitably - one instance was killed before they could be reunited and fight again over possession of their life and friends.

The Doctor Who universe also visited the idea in the 2011 two-part story "The Rebel Flesh"/"The Almost People", in which an electrical storm causes disposable artificial bodies (generated from organic material known as “flesh” and usually controlled by remote control as a form of protection against dangerous working environments) to become independently sentient, retaining the memories of their principals (who were in the system at the moment of disconnect). The story explicitly asks questions about the right to life of the created beings, but also about whether the “flesh” have any right to pursue the well-remembered (effectively, the previously experienced) life of their principals if those are deceased. This was also significant in the season arc plot as one of the series leads proved to have been inhabiting a flesh replica, without realising it, for an extended time.

Matter duplication, complete with memories, presents the exceptionally challenging question of what to do with the ‘spare’ (if this can even be identified). However it also begs the question of what actually constitutes human identity and whether the flesh and blood itself is actually a necessary component. The technology above all others which poses this question is computer or artificial intelligence. The concept here essentially builds on that of the Star Trek transporter - if an individual can be condensed to information during transport, then that information itself must be a sufficient representation of the person concerned, and it might be possible for a clone to exist simply as software. While most artificial intelligences in science fiction are original personalities constructed for their environment, a substantial fraction are created from the memory and personality imprints of humans (deceased or otherwise).

If these are recognised as self-aware and sentient, then they present a challenge to the identity of the individual, particularly if the original body does not survive or multiple copies of the encoded information are made (i.e. virtual transporter clones). This has been confronted directly in fictions such as Alastair Reynolds’ Revelation Space universe, in which the first individuals to be encoded as data were killed in the process, and their status as living computer intelligences was disputed. By the time in which the Revelation Space itself (novel, 2000) is set, strict laws regulate the production of sentient copies, which are ranked by the degree of independent thought permitted as alpha, beta or gamma simulations. Only one alpha-level persona of any individual is permitted to exist, as they are recognised as possessing full human rights and any duplicates would bring into question property ownership and identity itself.

While this is a well-developed system, in many other cases the right to existence and identity of the artificial intelligence clone is more closely questioned, particularly in the case of the common examples in SF of people encoded as AIs against their will, and often after their organic death. An interesting early example here is The Tunnel Under the World by Frederik Pohl (short story, Galaxy magazine, Jan 1955), in which not just one person but an entire destroyed town has been simulated under the illusion that they are still alive in order to test the effectiveness of advertising strategies. As one resident gradually recovers their memories, they have no doubt that they are the real individual until the very end of the story. As the story notes: “All the evidence had been before him. The automated factory, with its transplanted minds - why not transplant a mind into a humanoid robot, give it its original owner’s features and form? Could it know that it was a robot?”

 Who am I?

This question, ‘could it know that it was a robot?’, is just one aspect of a wider question: how do we know that we are ourselves at all? Is it possible (theoretically at least) to duplicate everything that makes a human themself, and, if so, would the duplicate have any more or less right to life than the original?

Over the decades, science fiction has explored this question in depth and attacked it from a range of directions [3]. The first and most fundamental is the hardest to answer - does a human have a soul which transcends their physical bodies? This is not a question physical or biological science is equipped to answer, and so science fiction with this focus tends to assume that the answer is unimportant and treat questions of cloning (physical or AI) and similar as an exploration of the ethics of pushing the limitations of science and knowledge. In other words, they explore not whether we can reproduce an individual but whether we should.

Of course this moral aspect is also a feature of much of the science fiction that explores the practicalities of identity reproduction. These often address the issue of whether our human consciousnesses are a product simply of an accumulation of memories or whether there is a physical aspect to it. If memories are sufficient to form identity, then artificial intelligence replication, or download to a very different or artificial body, could be plausible (assuming quantum limitations can be overcome). In that case each collection of data has the potential to form a new individual. 

Alternatively, some fictions suggest that personality may be tied to an organic body, such that the same personality will emerge from an exact clone (if those could be created without random mutation or damage to DNA), regardless of differences in life experiences and memories (as would be necessary for many clone-substitution plots). Experience based on identical twins (genetic clones) suggests this is unlikely to be the case, although stories of parallels between twins separated as infants frequently make the news and argue for a genetic component to personality. In this case, a duplicate mind in a different body, or existing as AI, could not be a true copy (but might yet be itself a conscious being). By contrast, others argue that personality is entirely environmental and suggest that a duplicate (even one genetically identical to the principal) begins to differentiate, as was the case in The Phantom of Kansas, as soon as its memories begin to diverge. The flip side of this is to ask whether an individual remains themself even if those life experiences or memories are destroyed (by injury or other processes).

As science advances, some of the moral and ethical exploration undertaken by science fiction of identity replication is becoming increasingly relevant. Cloning of mammals has now been demonstrated, although cloning of human beings is strictly forbidden under international law. Thus the production of a cloned human is arguably now theoretically possible, although the forced-growth and memory imprinting so common in science fiction still lay well out of reach. 

Also out of reach is the ability to make a complete recording of memory patterns and personality - indeed quantum uncertainty may make this a theoretical as well as practical impossibility. The ability of artificial intelligence to imitate humans is nonetheless rapidly developing. On the one hand, the so-called “deep fake” algorithm has shown the ability to reproduce physical appearance and voice in recordings or online interactions (a modern form of the master of disguise trope). On the other, large language models - while still a long way from self-aware - are now interacting routinely with people. Indeed, the idea of a digital afterlife of sorts is being explored by those hoping to provide a form of comfort in the shape of a digital replica of deceased persons. As of yet, there is no clear indication that the collection of information and machine learning associated with these efforts shows any sign of sentience or personality (indeed this falls under an entirely different class of science fictions). Given that we have little understanding of what forms our own personalities, it is challenging to say whether this will ever change.

In the majority of science fiction, characters experiencing personality duplication tend to one of two extremes: either they are determined to prove their own identity to an original (retaining property, friends, family and employment) or they are determined to differentiate themselves (adopting variations in name, hairstyle, weight or other characteristics as a form of rebellion or self-expression). Relatively few narratives exist in which duplicates exist harmoniously with their principals, suggesting that, for the majority of authors, the uniqueness of self is deemed to be a key aspect of human identity. As science and technology appears poised to threaten that uniqueness, the science fiction of ultimate identity theft continues to feel deeply relevant.