- "Guilty and innocent aren't our business, Mox. Killing who we're paid to is. Our. Business."
- ―Millie, to Moxxie
Millie is the tritagonist of Helluva Boss. She is Moxxie's wife and the bruiser of Immediate Murder Professionals (I.M.P), a startup assassination business that carries out its services in the living world.
Millie is a short Imp with a long, demonic tail with white markings. She has red skin, eyes with yellow scleras and black pupils, and long black eyelashes that extend beyond the sides of her hair.
She has two black horns with three thin white stripes and greyish-black hair worn in a messy bob style and bangs that cover half of her right horn. She has a beauty mark on her left cheek and a gap between her front teeth.
Millie's head is noticeably more human-like (although still without a nose) than a lot of other imps, lacking the pointed upper lip. Her teeth also usually appear flatter than the sharp conical teeth most demons have.
Her usual attire consists of black lipstick, a simple black choker, a cold-shoulder black crop top with gold buttons where the straps at the top meet the torso piece, torn black pants, fingerless black gloves, and black footwear that does not cover her hoof-like toes. During the episode Loo Loo Land, she wears sunglasses, a black suit and tie with a white shirt while guarding Stolas, just like Blitzo and Moxxie.
Millie also has a black tattoo in the shape of a heart on her right shoulder, and two white splotches on the insides and outsides of each of her elbows.
In the pilot, her hair had a white splotch mark near her right horn, although it was removed by the series proper.
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.
Also, as 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. She has a childlike-fondness of Loo Loo Land, triggered by familial memories of going there as a child.
- Millie speaks with a Southern accent. This was not constant in the Pilot, but could be heard occasionally.
- 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, as the game attendant pushing Moxxie away and attempting to flirt with her noticeably upset her.
- Mille mentioned her parents took her and her siblings to Loo Loo Land when they could manage it financially.
|Main characters||Hazbin Hotel||Charlie • Vaggie • Angel Dust • Alastor • Husk • Niffty|
|Helluva Boss||Blitzo • Millie • Moxxie • Loona • Stolas|
|Overlords||Alastor • Rosie • Valentino • Velvet • Vox|
|Supporting characters||Baxter • Cherri Bomb • Crymini • The Egg Bois • Exorcists • Helsa • Katie Killjoy • Lilith • Lucifer • Mimzy • Razzle and Dazzle • Seviathan • Sir Pentious • Tom Trench • Travis|
|Others||Arackniss • Barbie Wire • Collin • Eddie • Fat Nuggets • Fizzarolli • Robo Fizz • Henroin • Loo Loo • Martha • Mrs. Mayberry • Molly • Octavia • Ralphie • Roo • Stella • Tilla • Villa • Wally Wackford|