Emma Caulfield, who starred on several seasons of Buffy the Vampire Slayer as Anya the vengeance demon (with a golden naivety that made her a fan favorite), will be joining the cast of Supergirl as DC Comics character Cameron Chase, The Mary Sue reports.
WB's official description of the character on the show says this FBI agent has "little sympathy." The full description reads, "After her father’s violent murder, Cameron Chase decided to dedicate her life to law enforcement. Now a stern, no holds barred FBI agent, Chase’s weapons of choice are manipulation and manpower. With little sympathy, and plenty of suspicions, she pursues her targets with ruthless determination."
The character initially appeared in Batman #550 as a DEO agent - yes, the same DEO that's central to Supergirl. She had her own comic for ten issues, as well.