Millie is a female Imp that works at the Immediate Murder Professionals, a hitman agency that kills people on Earth. She is the group's close-range fighter. Millie works alongside her husband Moxxie, Blitzo and Loona. 
Millie is a cheerful and lively individual that genuinely enjoys her work. Beneath her meek exterior lies a bloodthirsty and violent personality. Millie is very protective of her husband Moxxie, and becomes violently angry when he gets insulted or hurt.
She has a Southern accent.