Hit-Monkey lived in the mountainous wilderness as part of a clan of other monkeys. Members of this clan took in a fugitive assassin, nursing him back to health with herbal remedies and hot springs. Hit-Monkey disagreed with this, knowing that someone would eventually come looking for the assassin. Once the nameless assassin regained his health, he began to hone his skills once more, practising on snowmen.
Hit-Monkey had studied this assassin, who had warned him against these evil ways. Hit-Monkey resorted to physical violence against the members of his clan over the continued presence of the assassin and was exiled to walk alone. He happened upon a group of soldiers in the woods who were looking for the assassin, and returned to the clan to give warning, but did not make it in time. The assassin and his clan were slain and Hit-Monkey sought vengeance, pick up the assassin's pistols and killing the soldiers.
His home and his tribe gone, Hit-Monkey set out on his journey as "a killer of killers" with a duffel bag full of guns. Searching for General Kato, the one who gave the orders to kill the nameless assassin he starts to kill every man Kato has engaged. After Kato realizes that a macaque is searching to kill him he hires Bullseye, his best man as a body guard.
The spirit of the deceased hit-man starts to guide him to the city were probably Kato is. Hideki Hiyshi, a politician involved in the plot too was his first target but Hit-Monkey shot his innocent assistant, and ran away crying. The ghost assassin scolded him. A thrown away news paper said that Kato's daughter was getting married so the perfect place for the hit was in Kato's garden. He has recently opposed Spider-Man and Deadpool.
Speculative existence: Due to both his skill as a hit-man leaving few witnesses and the fact that he is a macaque, his existence sounds too ridiculous to be true. This works to Hit-Monkey's advantage since few are willing to believe that a monkey is a credible threat.
Intelligence: Hit-Monkey has a human or near human intellect, and has been shown interacting with the world at large more like a human than a monkey.
Fighting Skills: As a monkey, Hit-Monkey naturally has above human agility and flexibility. Having opposable digits on his feet allows his to grip and wield guns while using his hands.