What defines "you"? The concept of identity, never mind the search for it, is a complicated question that fiction tries to answer. Beware though, fiction likes to throw us curve balls. Is it your memories? Those can be removed or altered. (Oh, are there ever so many ways.) How about your personality? Well, that changes over time naturally like it or not, but then again you can play someone else and find you like being them better. Is it your body? Less luck there, if it isn't a body swap it's a gender swap or something much worse. Does the Soul have anything to do with this? Are you still "you" if you reincarnate?