The cast of the 'Dexter' prequel series, 'Dexter: Original Sin,' has been revealed. Patrick Gibson (of 'Shadow and Bone'), Christian Slater (of 'Mr. Robot') and Molly Brown (of 'Senior Year') have been tapped to star in the prequel to the hit Showtime series that aired from 2006 to 2013. The series set in 1991 Miami will see Gibson play a young Dexter, as he goes from student to avenging serial killer. Slater will portray his father, Harry. And Brown will play his sister, Debra.