Michael Leonard Ontkean (born January 24, 1946) is a Canadian retired actor. Born and raised in Vancouver, British Columbia, Ontkean relocated to the United States to attend the University of New Hampshire on a hockey scholarship before pursuing a career in acting in the early 1970s.

He initially came to prominence portraying Officer Willie Gillis on the crime drama series The Rookies from 1972 to 1974, followed by lead roles in the hockey sports comedy film Slap Shot (1977) and the romantic comedy Willie & Phil (1980). In 1982, he had a starring role opposite Harry Hamlin and Kate Jackson in the drama Making Love, in which he portrayed a married man who comes to terms with his homosexuality. Ontkean continued to appear in films, such as Clara's Heart (1988) and Postcards from the Edge (1990) before being cast as Sheriff Harry S. Truman on David Lynch's Twin Peaks (1990–1991), the role for which he is best known.