He became known as secret agent Illya Kuryakin on the 1960s television series The Man from U.N.C.L.E. and as Dr. Donald Mallard on NCIS.
He worked as the assistant stage manager at the Glyndebourne Opera House after attending University College School.
He played operative Steel on ITV's Sapphire & Steel from 1979 to 1982.
He married Jill Ireland in 1957, and together they had three children.
He starred in the 1989 television thriller Mother Love with Diana Rigg.