Dexter

Dexter is a small capuchin monkey who lives at the Museum of Natural History. He is portrayed by monkey actor Crystal the Monkey.

Night at the Museum
Dexter first appears in the film Night at the Museum. A Capuchin Monkey on display in the Hall of African Mammals who at first seems cute and cuddly but is actually quite cheeky. When Larry Daley has his first Night Guard shift, Dexter causes a lot of trouble for him. Dexter tears up the list which Larry was using to help him, steals his keys and unlocks the storage gate releasing the exhibits into Central Park. He also bites Larry and urinates on him.

Night at the Museum: Battle of the Smithsonian
Dexter also appears in Night at the Museum: Battle of the Smithsonian.

Night at the Museum: Secret of the Tomb
Dexter appears in Night at the Museum: Secret of the Tomb.

Trivia
Trainers spent several weeks training Crystal to slap and bite Ben Stiller in the film.