Mark Feuerstein shines as Sara’s new husband, a mild-mannered professor of economics. However, as the season progresses, Feuerstein undergoes a brilliant chameleonic transformation. Playing the primary antagonist, the rogue CIA operative known as Poseidon, Feuerstein delivers a chillingly cold and intellectual performance that positions him as a worthy psychological rival to Michael Scofield. Augustus Prew as David "Whip" Martin

(Mark Feuerstein): Sara’s new husband, eventually revealed as the season's primary antagonist,

It is impossible to have a Prison Break "best cast" list without Robert Knepper. T-Bag remains one of television's most compelling villains, and in Season 5, he was given a fascinating redemption-adjacent arc.