David Keith McCallum, Jr. (born 19 September 1933) is a Scottish actor and musician. He is best known for his roles as Illya Kuryakin, a Russian-born secret agent, in the 1960s television series The Man from U.N.C.L.E., as interdimensional operative Steel in Sapphire & Steel, and Dr. Donald "Ducky" Mallard in the series NCIS.
McCallum was born in Glasgow, the second of two sons of Dorothy Dorman, a cellist, and orchestral leader (principal first violinist) David McCallum, Sr. When he was ten, his family moved to London.
McCallum won a scholarship to University College School, a boys' independent school in Hampstead, London, followed by the Royal Academy of Dramatic Art (also in London).