David McCallum's role as Dr. Donald "Ducky" Mallard on "NCIS" was integral to the show's success. Director James Whitmore Jr. revealed that the studio initially had reservations about casting McCallum, considering him an "old character actor." However, show creator Don Bellisario stood firm, insisting that McCallum was vital to the show. The Hollywood Reporter's recent oral history of "NCIS" was published on the same day as McCallum's passing, and it was noted that he was planned to have a limited role in the upcoming Season 21.