One of the more striking characters to emerge from the expansive "NCIS" universe was Abby (Pauley Perrette), the quirky Goth forensics expert. Unlike the stern military types that surrounded her, Abby was a free spirit, smiling and offering a fresh social perspective to her older colleagues. Abby appeared on the first 15 seasons of "NCIS" (it's currently on its 22nd), ultimately leaving her job -- and the show -- after a traumatic incident. 

Abby was sometimes a high-strung character, expressing a great deal of stress when one of her NCIS colleagues was injured. In the episode "One Step Forward", an MI6 agent named Reeves (Duane Henry) was killed trying to protect Abby from an assassin. Abby tracked down the assassin and fooled him into a confession using a ploy involving a coffee cup full of poison. She did manage to get a confession, and the assassin was apprehended, but Reeves' death...