Several fan-favorite characters have left NCIS over the years, including Abby, Ziva, Tony, and Gibbs. Abby left because the actress felt she couldn't work with Mark Harmon anymore due to a dispute. Ziva left because her character wasn't being written well, and the actress wanted better scripts. Tony left because the actor was burnt out and wanted a new challenge. Gibbs retired from the show, but may return in the future. Other characters like Todd, Bishop, Sloane, and Ducky also departed for various reasons. Overall, the departures were a mix of personal and creative decisions.