Deadpool

Deadpool is a Marvel comic book character who first appeared in the comic New Mutants #98". He has appeared in two video games, including X-Men Legends II: Rise of Apocalypse and Marvel: Ultimate Alliance'', where he appears as a playable character in both.

X-Men Legends II: Rise of Apocalypse
He first off appears as a boss in the game, though can later on be unlockable as a playable character. If you've unlocked Deadpool and later on go to fight Deadpool, the two will argue about who the real one is.