Olmos, best known for his role as William Adama in the Syfy series, will recur as a brilliant, charismatic professor of religious studies.
Olmos is the latest to join the Showtime drama for the upcoming sixth season. Colin Hanks has signed on to play Dexter's nemesis, and Off the Map star Aimee Garcia will play Batista's younger sister and Dexter's new nanny. Meanwhile, Mos (formerly known as Mos Def) will recur as an ex-con.
Production on Dexter begins Wednesday, with the series set to return this fall.