Who he is: Deadpool, a.k.a. Wade Wilson, Weapon XI
His power: That depends on the timeline. In the original XMU timeline, Wade Wilson has incredibly fast reflexes before he becomes Weapon XI, gaining a massive power upgrade that includes healing, teleportation, optic blasts, and two blades that retract from his forearms. In the new XMU timeline, Deadpool can heal from just about any wound or illness and has generally enhanced physical capabilities.
His story: No matter the timeline, Wade Wilson is a smartass who can’t keep his mouth shut. That might be why Col. William Stryker sews it shut in X-Men Origins: Wolverine when he turns Wade into Weapon XI, a soldier enhanced by a combination of different mutant powers. Wade initially meets Stryker when he’s part of his Team X mutant strike force with Wolverine and Sabretooth, and the two half-brothers face off against their old teammate when Stryker unleashes Weapon XI. He dies when his head is chopped off and his body falls into a nuclear reactor, but the timeline changes of X-Men: Days Of Future Past give Wade a new start and the opportunity to become the loudmouthed mercenary he was always destined to be.
Deadpool gives Wade Wilson a new origin story, and Stryker is nowhere to be seen. When he’s diagnosed with cancer, Wade volunteers for an experimental procedure that will give him superpowers, not realizing that the procedure is essentially a marathon of torture that will leave him scarred from head to toe when he’s finished. On the plus side, his cancer is wiped out by his new healing abilities. He escapes the clutches of Ajax, the mad scientist who gave him his powers, and stalks his ex-fiancée, Vanessa, when he’s not seeking revenge for his disfigurement. Vanessa is kidnapped after Deadpool’s first attempt to kill Ajax fails, so he reaches out to the X-Men for some help to save his girl and take out the bad guys. Wade’s mission is complete when he empties a round in Ajax’s skull, and he gets his happy ending with Vanessa when they make out in the wreckage of the aircraft that was just destroyed.
Played by: Ryan Reynolds
Currently, Deadpool is: Probably telling a joke while killing someone, or having Vanessa sit on his face.
Where will we see him next? He’ll definitely be in Deadpool 2, but he could also show up elsewhere in the XMU given his massive popularity.