David McCallum, who played Ducky on NCIS, was not initially seen as the right actor for the role, according to the show's writers. Former CBS Head of Casting Peter Golden revealed that the studio doubted McCallum's suitability, but creator Don Bellisario was adamant about casting him. McCallum, who portrayed the team's medical examiner and later became their part-time historian, was beloved by fans.

After his recent passing, NCIS stars paid tribute to his talent and professionalism.