NCIS has made a lot of cast changes over the years.

Many of the fan favorite stars are still part of the show, including David McCallum‘s Dr. Donald “Ducky” Mallard, however, there are a handful of stars who have left the show over the 20 seasons.

We’re taking a deep dive into just why the actors left the show, and some of the reasons include boredom, the insane working schedule, and more.

New episodes of NCIS air on Monday nights at 9pm ET on CBS.

Head inside to find out the reasons why all the main characters from NCIS left the show…