Colin Hanks and Mos, the actor and recording artist formerly known as Mos Def, were previously announced as guest stars for upcoming episodes of the show.
Best known for his work on TV's "Battlestar Galactica" and "Miami Vice," and in the films "Stand and Deliver," "Selena" and "The Green Hornet," Olmos will play a brilliant, charismatic professor of religious studies on "Dexter," Showtime said Tuesday.
Production on the new season is to begin Wednesday in Los Angeles.
Set to return to the cable network this fall, the series stars Michael C. Hall as a complicated blood-spatter expert for the Miami police department who moonlights as a serial killer.
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