David Keith McCallum, Jr. (born 19 September 1933) is a Scottish-American actor and musician. He first gained recognition in the 1960s for playing secret agent Illya Kuryakin in the television series The Man from U.N.C.L.E. and as interdimensional operative Steel in Sapphire & Steel. In recent years, McCallum has gained renewed international recognition and popularity for his role as NCIS medical examiner Dr. Donald "Ducky" Mallard in the American television series NCIS.