Ken Allen (1971–2000) was a Bornean orangutan at the San Diego Zoo. He became one of the most popular animals in the history of the San Diego Zoo 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 1988, the Wall Street brokerage firm Alex Brown & Company made a sizeable donation to the zoo and requested they name their "ugliest" orangutan after one of the firms equity traders.  (A conflicting source says Ken Allen was named after two zookeepers) During the 1980s, Ken Allen gained worldwide attention for a series of three escapes from his enclosure, which had been thought to be escape-proof. Ken Allen's ability to outwit his keepers, as well as 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, The Ballad of Ken Allen, was written about him.
During his escapes, first on June 13, 1985, again on July 29, 1985, and on August 13, 1985, Ken Allen would peacefully stroll around the zoo looking at other animals, and never acted violently or aggressively towards zoo patrons or other animals. Zookeepers were initially stumped over how Ken Allen had managed to escape.
Zoo staff began surveillance of his enclosure to try to catch him in the act, only to find that Ken Allen seemed to be aware that he was being watched for that very purpose. This forced zookeepers to go "undercover", posing as tourists to learn Ken Allen's escape route, but Ken Allen was not fooled. Moreover, other orangutans began following Ken Allen's lead and began escaping from the enclosure. Zoo officials eventually[when?] hired experienced rock climbers to find every finger, toe, and foothold within the enclosure and spent $40,000 to eliminate the identified holds.
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- Wilkens, John (26 December 1988), "Q: WHAT'S RED AND ESCAPES NINE TIMES? A: Ken Allen and the Zoo orangutans", The San Diego Union-Tribune, p. B.2, Factiva SDU0000020070630dkcq00i8d
- Orangutans, Resistance and the Zoo by Jason Hribal
- Meet Ken, San Diego Zoo’s Most Infamous (and Hairiest) Escape Artist by Joe Veix