Forrest soon transitioned to TV series such Playhouse 90, Lux Video Theater, and Alfred Hitchcock Presents. He became a fixture in the American Western genre. His classic Western TV roles included Gunsmoke, Bonanza, and The Virginian.
The actor signed under contract to the BBC in 1965 — as was more common in that era. He starred as John Mannering, an antique dealer/secret agent, in the hit British crime drama The Baron — the first color series on British TV.
From legendary TV producer Aaron Spelling, Forrest starred on the ABC action show S.W.A.T. for two seasons. The series was the basis for the 2003 film of the same name. Forrest's later TV roles included Dallas, Malibu, and Gunsmoke: Return to Dodge.
He is survived by his wife of 65 years, Christine, sons Michael, Forrest and Stephen and four grandchildren.