Maris Crane is Niles Crane's wife for much of the series, though she is never fully seen onscreen (much like Norm Peterson's wife, Vera, on Cheers). She is the most notable of the show's never-seen characters, and often the subject of many jokes. Her family name is not revealed on the series. Maris is immensely wealthy, much wealthier than Niles, as well as spoiled, dominating and neurotic. Many of the characters pointedly dislike her (to Niles' consternation), with Frasier contributing in the show's first episode, "Maris is like the sun...except without the warmth". In a further humorous vein, David Hyde Pierce passively describes Maris during a Montreal comedy performance (which he performs in-character) as "...a wife who's like a refugee from '[The] Taming of the Shrew'...

Maris was born in 1952, in Seattle. Her father was referred to as "The Commodore". She also has at least two sisters, one named Bree, who was born with only one nostril; she is mentioned as Frasier's date in one episode. As a child, Maris was overweight, but started losing weight and soon became very thin. She is described as small, very pale and pathologically emaciated; Roz originally mistook her for a hat rack, and Niles noted that she once sat on a whoopee cushion without setting it off.

Maris lived in her family's mansion, which has been in the family for four generations after they made their fortune from urinal cakes (but she fools people by telling them her fortune comes from timber). She met her husband, Niles, during his internship in Seattle when he stopped to help her as she was banging on the electric gates to get into her home. They were married three years later,[14] in 1986.

Maris makes only two onscreen "appearances": once in the episode "Voyage of the Damned" when her shadow is seen through a shower curtain, and again in "Rooms with a View", where she appears in Niles' memory, almost completely covered by bandages after surgery. In "The Seal Who Came to Dinner", the pass-code to Maris's seaside home is described as her "ideal weight", and "what she weighed at her débutante ball" during her pageant years. The series of numbers that Niles punched in would mean that Maris, at that time, was 45 pounds and 12 ounces. Aside from her low weight, Maris is subject to various medical problems: she has abnormally tight quadriceps, a rigid spine, a large number of very specific allergies, she cannot produce saliva, and has a slight webbing of her hands that made her self-conscious enough to shy away from their physical touch. She frequently travels to Europe for plastic surgery and expensive, eccentric health treatments.

In 1993 Maris and Niles refer Frasier to Daphne Moon (Niles' future wife) as a live-in physical therapist for Martin. Two years later, Maris goes to New York without telling Niles, who worries greatly. On her return, Niles stands up to Maris and she kicks him out of the house, beginning a two-year separation. Maris eventually reunites with Niles, but immediately has an affair with their marital therapist, Dr. Bernard Shenkman. In 1998. Niles finally files for divorce. In spite of the finalized divorce, Maris and Niles continue to be codependent for some time, until Niles finally breaks completely free, largely due to Daphne's aggravation. In 2003 Maris becomes romantically involved with a violent Argentinian polo player, Esteban de Rojo (Victor Alfieri), whom Maris kills in self-defense. Consequently, she is jailed for a few months on suspicion of murder. In 2004, shortly before her trial is scheduled to begin, she escapes to her family's private island from which she cannot be extradited, effectively stranding her for life.