Deadpool's real name in the comic book world is Wade Winston Wilson, and is considered an antihero—not unlike Batman, Daredevil, Wolverine, or the Punisher.
Deadpool is a mentally-unstable man who is facially disfigured, and for this reason he usually wears a mask, though it also doubles as a protector against others figuring out his identity.
He is also called, “Merc (mercenary) with a Mouth,” because he is quite talkative, with long streams of dialog, rambling, and vocal thoughts.
He is one of only a couple of comic book characters that will humorously narrate his thoughts or deeds to the comic reader.
This is technically called, breaking the fourth wall. And the character in the comics seems to know that he's a fictional character.
As with all superheroes, Deadpool has a super power: self-healing, similar to that of the X-Men's Wolverine character.
This was the result of the Weapon X program, and it prevents him from dying, though it is assumed that he feels the initial pains and aches of initial contact with fists, knives, bullets and the like.
These neurons constantly rejuvenating and replenishing within his brain also makes it hard for psychic and telepathic invasions to be deterred or confused.
This ability also makes toxins and drugs difficult to have an effect on him.
Because of this accelerated healing process, permanent injury is deterred, but this power that he has in his neurons causes psychosis and unstable mental health.
While psychosis can be considered a handicap, it benefits him also by giving him the ability to foreshadow the moves of his opponent—he knows the attack that is coming before it happens.
The character Taskmaster even had a hard time fighting Deadpool in Cable & Deadpool #38 because of Deadpool's erratic and unpredictable fighting patterns.