McCallum's obits say he's best known for ''NCIS,'' which I never watched. To me, he'll always be the ever-so-cool Illya Kuryakin on ''The Man From U.N.C.L.E.''
He was a man of many talents. Here's vintage video from that show where he briefly played guitar and sang ''Trouble'' with Nancy Sinatra, and it was a song he wrote!