Well known as Sheriff Harry S. Truman on the cult TV show Twin Peaks, he was previously known in another law enforcement role as Office Willie Gillis in The Rookies. His most notable film role was as Ned Braden in Slap Shot.
As a child actor, he appeared on a Canadian television program called Hudson's Bay. He grew up playing hockey and was the leading goal scorer his junior year at the University of New Hampshire.
He married Jamie Smith Jackson. His father was boxer and actor Leonard Ontkean and his mother was actress Muriel Ontkean.
He and Kyle MacLachlan frequently shared the screen while attempting to solve the murder of Laura Palmer in Twin Peaks.