Millie is the tritagonist of Helluva Boss. She is the bruiser of Immediate Murder Professionals (I.M.P), a startup assassination business that carries out its services in the living world.

PERSONALITY AND TRAITS
Millie is very lively and cheerful. Often with a smile on her face and rarely standing still, she is a clear extrovert and isn't afraid to speak her mind. Whether it's expressing her excitement or flipping off a coworker.
Millie is the bruiser of Blitzo's employees and seems to enjoy her job, it can be assumed she's tough and very violent as well. According to Moxxie, she is aggressive in the sack as well as her job. In "Murder Family" she appeared to be very unsympathetic about killing a family, only caring if it was what the client wanted, showcasing her dedication to her work. Despite this, she cares very much about her husband and apparently her family.

TRIVIA
* Viv has stated that she would change Millie's voice actor once the actual series premieres but would still keep her previous voice actor, Erica Lindbeck, to voice Loona. Later, actress and dancer Vivian Nixon, was hired to voice Millie.
* There is a large photo of what could possibly be Moxxie and Millie's wedding photo in the meeting room. In it, Millie is wearing a long strapless black dress and has wild hair that goes down past her hips, while Moxxie is wearing a white suit. It appears Blitzo has drawn over the photo in red marker to draw himself hugging them.
* This same photo seems to be in their living room although you can only see the bottom half and it doesn't have Blitzo's graffiti.
* In Vivziepop's 2019 short Holidaze as an ornament on a Christmas Tree, there is a tree carved with initials "M+M →B←" in a heart that alludes to her and Moxxie (and by extension Blitzo).
* While Millie seems to tolerate Blitzo's intrusions, she is not shown to be comfortable with other men flirting.
* Mille mentioned her parents took her and her siblings to Loo Loo Land when they could manage it financially.