 In season six, Mos Def was cast as Brother Sam, a convicted murderer turned born-again Christian, and Edward James Olmos and Colin Hanks guest-starred as Professor James Gellar and Travis Marshall, members of a murderous apocalyptic cult.Seasons seven and eight featured multiple guest stars, including Ray Stevenson as Ukrainian mob boss Isaak Sirko, a man with a personal vendetta against Dexter; Yvonne Strahovski as Hannah McKay, the former accomplice of a spree killer; Jason Gedrick as strip club owner George Novikov, also part of the mob; and Charlotte Rampling as Dr. Evelyn Vogel, a neuropsychiatrist who takes an interest in Dexter.Ronny Cox as the Tooth Fairy killer.