Milner died of heart failure at his home in Carlsbad, Calif., on Sunday, his wife told The New York Times.
Born in Detroit and raised in Seattle, Milner took an interest in acting at a young age, joining a children's theater group at the Cornish Playhouse. As a teenager, he moved to Los Angeles with his family, where he earned minor film roles and met Jack Webb, who gave him some work on his radio show Dragnet, which he later parlayed into guest spots on the TV show of the same name in the 1950s.
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After making several films in the 1950s, Milner found his greatest success on TV, first with the 1960 CBS series Route 66. Milner played Tod Stiles, who, after the death of his father, goes on a trip across the United States with his friend Buz Murdock (George Maharis). The show ran until 1964.
Milner followed that up in 1968 on the Webb-produced cop show Adam-12. He played veteran cop Pete Malloy who was partnered with rookie cop Jim Reed (Kent McCord). The show was a hit for NBC and lasted for seven seasons. Milner reprised his role on the short-lived The New Adam-12 during the 1990-91 TV season.
His other TV credits include The Swiss Family Robinson, Emergency!, Airwolf, Murder, She Wrote, and RoboCop: The Series. After retiring, he hosted a radio show about fishing called Let's Talk Hook-Up on XTRA 690.
He is survived by his wife Judy, three children and four grandchildren.