David McCallum, known for his role as Dr. Donald "Ducky" Mallard on NCIS, has passed away at the age of 90. The NCIS cast members, including Mark Harmon, Pauley Perrette, and Brian Dietzen, paid tribute to McCallum on social media. Despite McCallum's limited screen time in the show's recent years, his character had a lasting impact, with his quirky personality and expertise in autopsies. NCIS will return for season 21 and will honor McCallum and his legacy. The premiere date is uncertain due to the ongoing SAG-AFTRA strike.