A pompous, catty, effeminate, overrefined character with an upper-class English accent (which Frasier mentions on one occasion is an affected accent), believed by his coworkers to be in the closet, Gil claims to be married to Deb, a "Sarah Lawrence graduate and the owner of a very successful auto body repair shop" (and an Army Reservist), whom his co-workers had believed to be merely a pet cat. Gil claims to have had no idea everyone thought he was gay, even mentioning (or at least claiming) that he is married (to a woman) in a Season 5 episode (The Perfect Guy), and much of the humor related to the character stems from his adamant denial of his supposed sexual orientation, along with his general snarkiness. In one memorable episode, Frasier is disturbed to find that he is having heavily symbolic and vaguely sexual dreams about Gil. Frasier comes up with various interpretations, hoping to prove that the dreams don't actually mean he is attracted to Gil on some level, but in the end none of the interpretations are satisfactory.
Gil drives a red BMW with a red interior and is almost always seen wearing his trademark bow tie. It is also revealed in one episode that he wears an ankle bracelet. He claims to be a veteran of the armed services (he once refers to having "seen some cruel pranks in the Army"), and his taste buds are insured.
In the final season of the show, Gil's homosexuality begins to become more apparent. After a misunderstanding results in Frasier being publicly (and falsely) outed on the air after being spotted at a local gay bar, Gil attempts to coach Frasier on coming out, congratulating him on his first steps onto "the yellow brick road to pride and self-acceptance." During the episode's credits, Gil himself is seen covertly entering the gay bar in question, Bad Billy's.
His last appearance is in the show two part finale Goodnight, Seattle where he is seen along with Kenny Daly, Roz, Daphne, Bulldog, Bebe, Martin, Ronee, Niles and the rest of the KACL staff watching Frasier do his Farewell Speech
The character is named in honor of the real-life Gil Chesterton, a former journalism teacher (now retired) at Beverly Hills High School. One of the series' producers, Christopher Lloyd, was Chesterton's student years ago, and Lloyd evidently felt naming a character in a hit sitcom would be a nice homage to his former teacher.