Deadpool aka Wade Winston Wilson first appeared in The New Mutants #98 (cover-dated February 1991). Initially, Deadpool was depicted as a super-villain but later evolved into his more recognizable antihero persona. Although he is a dark character, he is best known for his irreverent sense of humor and constantly breaking the fourth wall — Deadpool knows that he is a fictional comic book character.

Deadpool is depicted as having a regenerative healing factor, which not only prevents him from being permanently injured through enhanced cell regeneration throughout his body, but also causes psychosis and mental instability. It is thought that while his psychoses are a handicap, they are also one of his assets as they make him an extremely unpredictable opponent. Taskmaster, who has photo-reflexive memory which allows him to copy anyone's fighting skills by observation, was unable to defeat Deadpool due to his chaotic and improvised fighting style. Taskmaster has also stated that Deadpool is an expert at distracting his opponents.

The character, known for his talkative nature, has been nicknamed the "Merc with a Mouth".

In 2015, Deadpool co-creator Fabian Nicieza pushed back against fan theories about Deadpool's sexuality with a Tweet.

Regardless of phrasing, Deadpool clearly belongs under the bi umbrella. His attractions are not limited to one sex and he is proud of his diverse attractions.

In the Marvel Cinematic Universe, Deadpool is played by Ryan Reynolds. 

Image of Deadpool from the Marvel movies, looking shocked with his hands on his face.
Image/Marvel