The voice actor for which Portal 2 character was not a TV or film actor prior to the game?

The answer is GLaDOS. Prior to Portal 2, GLaDOS was voiced by actress Ellen McLain, who had primarily worked in theater and opera. McLain's portrayal of GLaDOS in the game elevated the character to iconic status, despite not having previous experience in TV or film acting. McLain's captivating performance as GLaDOS in Portal 2 showcased her immense talent and solidified GLaDOS as one of gaming's most memorable characters.