24. Nina Myers, '24'
Move over, Benedict Arnold: America has a new top traitor in town. Over the course of the show's first season — ahem, first day — Nina went from heroic CTU operative to hated, murdering mole, serving as Jack Bauer's archenemy for two more seasons before finally receiving the same lethal punishment she'd doled out to so many others. Actor Sarah Clarke gave Nina a steely-eyed glare and an equally unyielding personality, separating her from the jittery, guilt-ridden double agent Nicholas Brody whom 24 staffers Howard Gordon and Alex Gansa would go on to create for Homeland.