Wade Winston Wilson was the son of a mentally ill mother and army general, who cause him to be a teenage delinquent. After being kicked out of the army, he became a mercenary. Eventually, he got a deadly form of cancer. So he joined a government program called "The Weapon X Project". He gained regenerative healing, that cured the cancer, but was considered a failure and was put under the "care" of Doctor Killebrew, who made them play his "game" Dead pool, where inmate bet on how long person will last though painful and deadly genetic experiments his did to them. By some miracle Wade survived and escape. He returned to being a mercenary and took the name Dead Pool. This time he had many encounters with mutants including the X-men, the shape shifting Copycat, the telepathic / telekinetic Cable and Siren (who has the Banshee's powers), who he had a crush on. Dead Pool is one of the few Marvel characters that knows he's in a comic.
X-men Ultimate Guide