Homer and his wife, Marge, have three children: Bart, Lisa, and Maggie. As the family's provider, he works at the Springfield Nuclear Power Plant. Homer embodies several American working class stereotypes: he is crude, overweight, incompetent, clumsy, lazy and ignorant; however, he is also fiercely devoted to his family. Despite the suburban blue-collar routine of his life, he has had a number of remarkable experiences.

In the shorts and earlier episodes, Castellaneta voiced Homer with a loose impression of Walter Matthau; however, during the second and third seasons of the half-hour show, Homer's voice evolved to become more robust, to allow the expression of a fuller range of emotions. He has appeared in other media relating to The Simpsons – including video games, The Simpsons Movie, The Simpsons Ride, commercials and comic books – and inspired an entire line of merchandise. His catchphrase, the annoyed grunt "d'oh!", has been included in The New Oxford Dictionary of English since 1998 and the Oxford English Dictionary since 2001.

Homer is one of the most influential fictional characters on television, having been described by the British newspaper The Sunday Times as "the greatest comic creation of [modern] time". He was ranked the second greatest cartoon character by TV Guide, behind Bugs Bunny, and was voted the greatest television character of all time by Channel 4 viewers. For voicing Homer, Castellaneta has won four Primetime Emmy Awards for Outstanding Voice-Over Performance and a special-achievement Annie Award. In 2000, Homer and his family were awarded a star on the Hollywood Walk of Fame.

Homer Simpson is the bumbling husband of Marge and father of Bart, Lisa and Maggie Simpson. He is the son of Mona and Abraham Simpson. Homer has held over 188 different jobs in the first 400 episodes of The Simpsons. In most episodes, he works as the Nuclear Safety Inspector at the Springfield Nuclear Power Plant, a position he has held since "Homer's Odyssey", the third episode of the series. At the plant, Homer is often ignored and completely forgotten by his boss Mr. Burns, and constantly falls asleep and neglects his duties. Matt Groening has stated that he decided to have Homer work at the power plant because of the potential for Homer to create havoc. Each of his other jobs has lasted only one episode. In the first half of the series, the writers developed an explanation about how he got fired from the plant and was then rehired in every episode. In later episodes, he often began a new job on impulse, without any mention of his regular employment.

The Simpsons uses a floating timeline in which the characters do not physically age, and, as such, the show is generally assumed to be set in the current year. Nevertheless, in several episodes, events in Homer's life have been linked to specific time periods. "Mother Simpson" (season seven, 1995) depicts Homer's mother, Mona, as a radical who went into hiding in the mid-1960s following a run-in with the law; "The Way We Was" (season two, 1991) shows Homer falling in love with Marge Bouvier as a senior at Springfield High School in the 1970s; and "I Married Marge" (season three, 1991) implies that Marge became pregnant with Bart in 1980. However, the episode "That 90's Show" (season 19, 2008) contradicted much of this backstory, portraying Homer and Marge as a childless couple in the early 1990s.

Homer's age has increased as the series developed; he was 36 in the early episodes, 38 and 39 in season eight, and 40 in the eighteenth season, although even in those seasons his age is inconsistent. During Bill Oakley and Josh Weinstein's period as showrunners, they found that as they aged, Homer seemed to become older too, so they increased his age to 38.

Matt Groening conceived Homer and the rest of the Simpson family in 1986 in the lobby of producer James L. Brooks' office. Groening had been called in to pitch a series of animated shorts for The Tracey Ullman Show, and had intended to present an adaptation of his Life in Hell comic strip. When he realized that animating Life in Hell would require him to rescind publication rights, Groening decided to go in another direction, and hurriedly sketched out his version of a dysfunctional family, naming the characters after members of his own family. Homer was named after Groening's father. Very little else of Homer's character was based on him, and to prove that the meaning behind Homer's name was not significant, Groening later named his own son Homer. Although Groening has stated in several interviews that Homer's namesake is his father, he also claimed in several 1990 interviews that a character in the 1939 Nathanael West novel The Day of the Locust was the inspiration for naming Homer. Homer's middle initial "J", which stands for "Jay", is a "tribute" to animated characters such as Bullwinkle J. Moose and Rocket J. Squirrel from The Rocky and Bullwinkle Show who got their middle initial from Jay Ward.

Homer made his debut with the rest of the Simpson family on April 19, 1987, in The Tracey Ullman Show short "Good Night". In 1989, the shorts were adapted into The Simpsons, a half-hour series airing on the Fox Broadcasting Company. Homer and the Simpson family remained the main characters on this new show.

The entire Simpson family was designed so that they would be recognizable in silhouette. The family was crudely drawn, because Groening had submitted basic sketches to the animators, assuming they would clean them up; instead, they just traced over his drawings. Homer's physical features are generally not used in other characters; for example, in the later seasons, no characters other than Homer and Lenny have a similar beard line. When Groening originally designed Homer, he put his initials into the character's hairline and ear: the hairline resembled an 'M', and the right ear resembled a 'G'. Groening decided that this would be too distracting though, and redesigned the ear to look normal. He still draws the ear as a 'G' when he draws pictures of Homer for fans. The basic shape of Homer's head is described by director Mark Kirkland as a tube-shaped coffee can with a salad bowl on top. Bart's head is also coffee can shaped, while spheres are used for Marge, Lisa and Maggie. During the shorts, the animators experimented with Homer's mouth movements when talking and at one point his mouth would stretch out back "beyond his beardline", but this was stopped when it got "out of control." In some early episodes, Homer's hair was rounded rather than sharply pointed because animation director Wes Archer felt it should look disheveled. Homer's hair later evolved to appear consistently pointed. During the first three seasons, Homer's design for some close-up shots included small lines which were meant to be eyebrows. Matt Groening strongly disliked them and they were eventually dropped.

In the season seven (1995) episode "Treehouse of Horror VI", Homer was computer animated into a three dimensional character for the first time for the "Homer3" segment of the episode. The computer animation directors at Pacific Data Images worked hard not to "reinvent the character". In the final minute of the segment, the 3D Homer ends up in a real world, live-action Los Angeles. The scene was directed by David Mirkin and was the first time a Simpsons character had been in the real world in the series. The episode "Lisa's Wedding" (season six, 1995) is a flashforward, set fifteen years in the future and Homer's design was altered to make him older. He was redesigned to be heavier, one of the hairs on top of his head was removed and an extra line was placed under the eye. A similar design has been used in subsequent flashforward episodes.