Wade Wilson/Deadpool (Ryan Reynolds)
When your defining characteristic is that you are bug nuts insane, it’s really hard to pin down your origin, and that couldn’t be truer for Wade Wilson/Deadpool, with his mental condition making his personal history something of a twisted pretzel to navigate (at one point his nemesis T-Ray claims he’s the real Wade Wilson, and Deadpool is an impostor). But the facts we do know are these: Wade Wilson was a mercenary for hire who, when he contracted cancer, was taken in by a branch of the Weapon X program (yes, the same shadowy, secret organisation that gave Wolverine his adamantium bones), who made him a test subject in a project looking to create an artificial helping factor derived from, you guessed it, Wolverine. The implantation was a success, it arrested his illness and granted him the ability to constantly regenerate his body’s cells.
Due to this healing factor he can never be permanently injured, or even die (if you cut off his head, it’ll just reattach itself when close enough to his body). But the constant regeneration also affects him mentally, with his neurons also constantly regenerating, leading to numerous psychosis (mainly that he is aware he is a fictional character, and constantly breaks the fourth wall). This deemed the experiment failure in the eyes of Weapon X, who send Wade to the Hospice with the rest of the rejects, where he was tortured and ultimately escaped. The one part of his body which he can’t heal, attributed to amenable block, his his face, which is why he constantly keeps it cover with his signature mask.
Weasel/Jack Hammer(T.J. Miller)
While Deadpool has had many sidekicks in his long history, from the mysterious Blind Al, the cowardly Bob, Agent of Hydra (who we’ll never likely see due to the rights to Hydra being with Marvel Studios. Shame, he’s awesome), and even the disembodied head of a zombie version of himself from another dimension, nicknamed Headpool. But the one constant by his side is Weasel. A dealer in hi-tech arms and information broker, Weasel met Deadpool not long after the mercenary parted ways with Weapon X (in bloody fashion, of course), and soon the pair became best friends, Weasel providing weapons and intelligence to the Merc with a Mouth on his many, bloody missions.
Copycat/Vanessa Carlyse (Morena Baccarin)

Ajax/Francis (Ed Skrein)
As head enforcer for Dr. Killbrewe, who conducted vile experiments on the Weapon X ‘washouts', the man known only as Francis let his boss experiment on him to make him the ultiamte soldier. With his nerves removed, he can’t feel pain. He was also given implants to enhance his strength and speed, which he used to torture the inmates of the Hospice whenever they stepped out of line, getting immense pleasure out of picking on Wade in particular. Finally given the order to kill him, Francis removed Deadpool’s heart which saw his healing factor finally kick in. Deadpool then hunted Francis down and seemingly killed him. He resurfaced years later, now named Ajax, and became quite the thorn in the side for Deadpool, swearing revenge on him, and killing many serving members of Weapon X as a way to do so.
Angel Dust (Gina Carano)
Negasonic Teenage Warhead (Brianna Hildebrand)
Blind Al (Leslie Uggams)
One of Deadpool’s most enduring supporting characters, the name says it all Blind Al has a bizarre relationship with the Merc with a Mouth acting as his friend, prisoner, and housekeeper, often punishing her by putting her in “The Box”, a small room filled with sharp objects. With her past never fully revealed, she stuck with Deadpool and took his abuse in attempt to redeem him, hoping in turn to redeem herself for dark deeds she took part in her younger life. At times, she was almost like a parent to him, and even though their relationship was antagonistic most of the time, they did genuinely care for each other. When Deadpool wasn’t pranking her, of course.