Adam Campbell received advice from David McCallum after joining NCIS as a young Donald “Ducky” Mallard “One thing he said was, 'Don't try to do an impression of me.' Which was really helpful," the 45-year-old actor said on the NCIS: Partners & Probies podcast McCallum, who died at 90 in 2023, played the beloved medical examiner for 20 seasons Adam Campbell received advice from a legend.