To the older generation, he is perhaps best known for his portrayal of "U.N.C.L.E. agent Illya Kuryakin" in the TV Show The men of U.N.C.L.E.
For everybody else he is currently starring in NCIS as "Dr. Donald "Duckie" Mallard" on the CBS.
Was considered as a potential Doctor in Doctor Who.
Son, Valentine McCallum, is a respected guitarist and session musician, recording and performing with artists Jonatha Brooke, Vonda Shepard and Sheryl Crow.
One of the first Brit actors to study the Method style of acting.