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Trinity Killer (John Lithgow)

John Lithgow as Arthur Mitchell (Season 4, episode 12-finale) - Photo: Randy Tepper/Showtime - Photo ID: dexter_412_1477

'Dexter' Villains: The Enemies List

Eight seasons of "Dexter" has meant a lot of blood and a lot of killing, and not all of that gore has come courtesy of Dexter Morgan. He is the serial killer who hunts other serial killers, after all, and our man Dex has had more than his fair share of worthy adversaries throughout the years. With the "Dexter" series finale unfolding on Sept. 22 at 9 p.m. on Showtime, we look back at some of Dexter's most dastardly challengers, including a few who are thriving elsewhere in TV land these days. — Kimberly Potts, Yahoo TV