Seth Gilliam (November 5, 1968) is an American screen and stage actor. He is most known as Father Gabriel on AMC's post-apocalyptic series The Walking Dead, first appearing in Season 5.He is also known for his HBO television roles, first as corrections officer-turned-prisoner Clayton Hughes on Oz, and later as Baltimore police detective promoted to Sergeant, Ellis Carver on The Wire. On both of these series, he co-starred with Lance Reddick and J.D. Williams. Another of his major recurring roles was on the TV series Teen Wolf as Dr. Alan Deaton.He had a recurring role during the seventh season of The Cosby Show as Aaron Dexter (boyfriend of Erika Alexander's character Pam), Law and Order: Criminal Intent, and Law and Order: Trial by Jury. He's had a number of guest roles in other shows such as CSI: Miami, Nurse Jackie, Skins, Person of Interest, The Good Wife, and Bull.His feature film credits include his role as Sergeant Steven Altameyer in Courage Under Fire (1996) and Private Sugar Watkins in the action movie Starship Troopers (1997). His other films include Personal Velocity (2002), Did You Hear About the Morgans? (2009), and Still Alice (2014).