Ken Allen never acted violently or aggressively towards zoo patrons or animals except for another orangutan called Otis, whom he despised. During his third escape, he was caught stoning Otis and had to be led back to his enclosure. After the attack, the zoo temporarily placed him in solitary confinement.

Kenneth Allen (February 13, 1971 – December 1, 2000) was a male Bornean orangutan at the San Diego Zoo in California, United States. He became one of the most popular animals in the zoo's history because of his many successful escapes from his enclosures. He was nicknamed "The Hairy Houdini".

Ken Allen was born in captivity at the San Diego Zoo in 1971. In 1985, he gained worldwide attention for a series of escapes from his enclosure, which had been thought to be escape-proof. During some of his escapes, his female companions joined him. Ken Allen's ability to outwit his keepers and his docile demeanor during his escapes resulted in fame. He had his own fan club and was the subject of T-shirts and bumper stickers (most reading "Free Ken Allen"). A song about his escapades, "The Ballad of Ken Allen", was written by Dennis Gersten.