The evil monkey lives in Chris's closet. As his name suggests, he is filled with malice towards all, particularly Chris. Chris is the only member of the Griffin family who is aware of the presence of the monkey in the house, the others laughing at the notion that Chris has a monkey in his closet. The monkey was first seen in "Dammit Janet!".
Until Chris captured him and showed the Griffin family in "Hannah Banana", the evil monkey had rare encounters with other characters other than Chris throughout the entire series: the Evil Monkey's wife, the monkey she was sleeping with, Chris' pimple, Brian's son Dylan, Peter, who mistook him for Meg and Herbert who slept through his encounter.
The evil monkey was accompanied by a human female on the red carpet to see Stewie Griffin: The Untold Story and pulled off his trademark pose on request. The pose was also used in "Road to Germany" when Stewie and Adolf Hitler were copying the mirror scene from Marx Brothers. Chris once sung a song about him, titled "Evil Monkey Song", with his heavy metal band. In "Model Misbehavior", the evil monkey is shown relaxing after the Griffin's departure by smoking a joint and listening to Foghat on vinyl through headphones on Chris' bed. In "Play It Again, Brian", he tried to scare Chris, only to find he wasn't there, just Herbert who was asleep. The Monkey then slowly closed the closet door. In "It Takes a Village Idiot, and I Married One", He becomes a member of the Jehovah’s Witnesses, and is shown with an issue of The Watchtower, a magazine published by and closely associated with the Witnesses and a chain smoker.
In "The Former Life of Brian" he is beaten up by Brian Griffin's son Dylan Flannigan, allowing Chris finally to have access to his closet, where he discovers a very large quantity of feces. He was briefly seen in "420" during the performance of "A Bag of Weed", emerging from a portable toilet with a joint.
In "Hannah Banana", Chris captures him to prove his existence to his parents. It is revealed he points at people to strike up a conversation, suffers from a copper deficiency which explains why his arm shakes, and the sinister expression is merely the face he makes while he's thinking. He explains to the family his true origins and how he never intended to harm Chris. It is revealed he is not actually evil, but was rather in a "bad place" in his life after he caught his wife in bed with another monkey in "Ready, Willing, and Disabled". This caused him to become depressed, which ultimately resulting in him losing his job and his house, which is why he moved into Chris's closet. It is thought that Evil Monkey was once a lawyer due to the nature of his clothing in the scene where he caught his wife.
Although Chris at first doesn't trust him, the two develop a close friendship, bordering on a father/son relationship. After helping Chris and Peter repair their relationship, the Evil Monkey; or rather just Monkey now, decided it was time to move on. As such he doesn't live in Chris's closet anymore, but rather now lives in Jake Tucker's house. Like with Chris, the Monkey lives in Jake's closet and at unexpected moments opens the doors, points and shakes with a sinister expression on his face, frightening Jake. It is explained that he intends to help Jake and Tom Tucker, who like Peter and Chris have a less than pleasant relationship.
In Something, Something, Something, Dark Side, he appeared as a Mynock in the asteroid cave.