If you have yet to see the first episode of season one of Disney’s Loki series, this essay contains spoilers. This episode presents some of the metaphysics of the MCU: there are many timelines (alternate realities) and variants of people, such as Loki and Deadpool, exist in some of them.
Loki is, obviously, the main character of Loki. In fact, he is two main characters: the anti-hero Loki and the hero-anti Loki (the villain). Since the metaphysics of the MCU includes time travel, this entails that the same person can be at different places at the same time. They can even fight, as happened with Captain America. While this is a metaphysical mess, this means time travel can be used as a multiplier: a person can time it so different versions of themselves arrive at the same place at the same time. So, for example, Loki could show up to fight an enemy at a set time and arrange for himself to go back or forwards in time ten times and end up with eleven of himself to overwhelm the foe. This, of course, leads to the usual paradoxes and problems of time travel. A future Loki could tell a distant past Loki about things that a middle past Loki did not know, but then the middle past Loki would know it. While this is even more of a mess, the time travelling Lokis could remain there in that time and start their own lives or perhaps travel back to a more distant past over and over to create a vast army of Lokis that meet up at a future time to do whatever it is that his character arc directs him to do.
Such time travel has various other problems. A point often made in time travel tales is the importance of not changing the past. Some sci-fi stories do allow a change in the past to change the future; other stories simply make it so that whatever the time travelers do is what happened anyway. That is, they make no change in the past because what they do is what they did and will always done did (Star Trek IV implies this). The classic grandfather paradox falls into this family of problems: if a person goes back to the past and changes things that impact their ability to go to the past (such as killing their grandfather), then they could not go back to change the past and hence the past would be unchanged and so they could go back to the past. But they could not, because if they made that change then they could not go back. And so on. In fiction, the writers simply write whatever they wish, but this does not address the matter of how this would all “really” work.
There is also the problem of personal identity: in the metaphysics of the MCU variants arise and a new timeline branch could presumably also spawn variants that create additional branches. As there are multiple Lokis in the show, they both spawned off the main timeline. Perhaps one Loki “divided”, or one Loki “split” from the other Loki. Or perhaps there are three (or more) Lokis: there is the Loki who remained on the timeline and was killed by Thanos. There is the Loki who escaped from the Avengers because of their time heist (the anti-hero of the show) and the third Loki who is the villain. Because of time travel, the third Loki might have split from the second Loki in the future. As always, time travel is a mess.
Having multiple Lokis does create the usual problems for personal identity. After all, what provides personal identity is supposed to make a person the person they are, distinct from all other things. As such, it would seem to be something that should not be able to be duplicated. Otherwise, it would not be what makes an entity distinct from all other things. If there are two Lokis in a room, there must be something that makes them two rather than one. There must also be something that makes each of them the Loki they are. But is this true?
One approach is taking inspiration from David Hume’s theory of personal identity. After he argues a person is a bundle of perceptions, he ends up saying that, “The whole of this doctrine leads us to a conclusion, which is of great importance in the present affair, viz. that all the nice and subtle questions concerning personal identity can never possibly be decided, and are to be regarded rather as grammatical than as philosophical difficulties.” While this might be true, it does not satisfy. But it does provide a way of resolving a room full of Lokis: it’s a matter of grammar.
Another approach is trying to sort out the metaphysics of personal identity in the context of time travel. After all, time travel requires that entities can be multiply located while personal identity would seem to forbid duplication of what individuates. The reason time travel requires multiple location is that something from one time travels to another time and the matter or energy that makes up what travels will also be present when it arrives. So, the same thing will be in two places at the same time; something that is not normally possible. But one could accept the existence of metaphysical entities that allow this.
Yet another approach, and one that seems to match how the timelines were presented in the show, is that a branching creates an entire new reality that is similar but not identical to the first. This would also duplicate the people, perhaps creating them ex nihilo. So, the various Lokis would be similar people, but not the same person.