"NCIS" actor David McCallum, who portrayed the iconic character Ducky for 20 years, was not initially considered the right actor for the role, according to the show's writers. The studio had doubts about casting McCallum due to his age and British nationality. However, show creator Don Bellisario insisted on casting him, and McCallum went on to become a beloved part of the show. Following McCallum's recent death at the age of 90, several "NCIS" stars paid tribute to him on social media.