Deborah Theaker (born April 6, 1964) is a Canadian actress.

Theaker was born in Moose Jaw, Saskatchewan, Canada. She is best known as Casey Edison on the Lucasfilm science fiction satire Maniac Mansion which ran from 1990 until 1993. In 1985, Theaker graduated from the University of Saskatchewan and later moved to Toronto, where she became a member of The Second City's resident company. Since 1987, She has played roles in various television shows and movies, including The Kids in the Hall, Joey, Howie Mandel's Sunny Skies, Desperate Housewives, Rat Race, Entourage, Bones, and Lemony Snicket's A Series of Unfortunate Events as well as the Stargate SG-1 season-eight episode entitled "Citizen Joe." She is a member of Christopher Guest's cinematic repertory company and has appeared in four films and multiple commercials for director Guest. Theaker guest starred in the third season of the acclaimed sitcom Husbands.