Mildred is Guy Montag's wife, but they do not act as a normal couple. She is distant, self-centered, and is completely absorbed in her "TV Family". She doesn't remember much about Guy, including the day they met. Mildred doesn't care much for anything outside of her parlor walls, seashell ear radio, or driving her car, the beetle, at top-notch speeds.
Mildred is physically described by Montag, "Her hair burnt by chemicals to a brittle straw, her eyes with a kind of cataract unseen but suspect far behind the pupils, the reddened pouting lips, the body as thin as a praying mantis from dieting, and her flesh like white bacon. He could remember her no other way." (p.48)
Early in the book, she attempts suicide by taking a bottle of sleeping pills. This shows that perhaps she believes her life is painful, which would explain her addiction to her parlor TV.
She eventually betrays Montag after she refuses to accept her husband's understanding of books. She reports him to the firemen. After Captain Beatty confronts Guy, Mildred drives away and leaves Guy forever, never looking back.