David McCallum, known for his role as Ducky the medical examiner on "NCIS" to younger viewers and as co-star with Robert Vaughn in "The Man From U.N.C.L.E." to their grandparents, has passed. His rep confirmed that the actor passed from natural causes. A previously announced 20th anniversary "NCIS" marathon will now include an "In memoriam" card in remembrance of McCallum, according to CBS. Along with his decades-long career on television, Mccallum also appeared in many notable films, including "The Greatest Story Ever Told," "The Great Escape, "Mosquito Squadron," "Freud" and "A Night to Remember." McCallum was 90.