*Mildred "Millie" Knolastname is an assassin at I.M.P, Moxxie's wife, and one of the main protagonists of Helluva Boss.

She is the exciteful powerhouse of the I.M.P gang who always fights alongside Moxxie.

Millie is a short imp with red skin and a long devilish tail. She has a pair of thin white-striped black horns and short messy, bob cut-styled charcoal hair with bangs. Her eyes have yellow sclera and long, thick eyelashes protruding from them, with a small beauty mark under the right eye. Her front teeth have a gap as well.

She also has a black heart tattooed on her right shoulder, and makeup which consists of shimmering dark red eyeshadow, thick black mascara, and black lipstick on her lips. She also has two white spots on her upper right arm, one on her upper left leg, two on her tail, and one on the tip of her tail.

Millie's attire is all-black with a tint of yellow, which consists of a black choker around her neck, a cold-shoulder black midriff-top with the straps being held by two golden-yellow buttons, black fingerless gloves, black torn denim-pants and black toeless footwear, which exposes her hoof-like toes.

Millie is a very lively and cheerful individual. Often with a smile on her face and rarely standing still, she is a clear extrovert and is not afraid to speak her mind. This is regardless to whether it's expressing her excitement or flipping off a co-worker.

As the bruiser for I.M.P, she is shown to enjoy her job. Her meek exterior appearance belies a tough and very violent skillset. This is highlighted during a conversation Millie once had with her mother and sister. 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 possibly innocent target, only caring if it was what their client wants, showcasing her dedication to her work, and her ruthlessness. Furthermore, she is also shown to be somewhat defensive of her work, expressing annoyance whenever anyone implies that freelance work doesn't pay well.

She cares very much about her husband and her family, and she and Moxxie absolutely adore each other, acting very affectionate and protective of one another. She has a childlike fondness of Loo Loo Land, triggered by familial memories of going there as a child, and gets easily excited by all the merchandise.

Millie will become vicious and violent whenever someone harms Moxxie, to the point of going feral. Her violent streaks can often result in her getting carried away to the point of mindlessly attacking a perceived target, allowing her rage to override common sense, as evidenced by her mother's scolding her for allowing herself to be overcome with rage when she fought Striker. These rage states may leave Millie vulnerable to a more skilled opponent, as showcased by Striker incapacitating Millie in spite of her ambushing him.

In "Unhappy Campers", it is revealed that she has some issues about how she sees herself, confessing how she sometimes does not feel appreciated enough and how she wants to be seen more than just a "killing machine", stating how it feels nice to feel important and hear the cheers and applause of people every once in a while rather than the occasional screams of agony from her victims. In "Ghostf**kers", she had once suffered from insecurity over how she feels like she's seen as a "Wrathian who's only good for their muscle" until she met Blitzo who changed her life for the better.

Unlike her husband, Millie seems to be not much bothered by Blitzo's constant attempts to become their "third", even if sometimes she wants to be alone with Moxxie. In "Ghostf**kers", it's revealed that, unlike most others, Millie doesn't see Blitzo as someone who messes with others' lives, as it was thanks to him that she got a better life than the one she had, including falling in love with Moxxie and marrying him. This leads Millie to be the only one to be able to snap Blitzo out of his depression after the latter's falling out with Stolas.

She is about 27 in hell years.

Her sexuality is straight.*