As a test subject in the same Weapon X program that had previously given Wolverine his adamantium claws and skeleton, Wade Wilson received a healing factor that prevented his cancer from killing him.
Wade soon escaped the program and became a freelance mercenary using the name Deadpool, working for various criminal organizations. At times he has teamed up with heroes as well, but these attempts at "being a good guy" rarely stick for long.
Wade is mentally unstable, though whether this is a normal state or is caused by his constant state of hyper-regeneration is unknown. One side effect of his mental state is the belief that he is not a real person but actually a character in a comic book.