The Simpsons are a family who live in a fictional "Middle American" town of Springfield. Homer, the father, works as a safety inspector at the Springfield Nuclear Power Plant, a position at odds with his careless, buffoonish personality. He is married to Marge Simpson, a stereotypical American housewife and mother. They have three children: Bart, a ten-year-old troublemaker; Lisa, a precocious eight-year-old activist; and Maggie, the baby of the family who rarely speaks, but communicates by sucking on a pacifier. Although the family is dysfunctional, many episodes examine their relationships and bonds with each other and they are often shown to care about one another. The family owns a dog, Santa's Little Helper, and a cat, Snowball V, renamed Snowball II in "I, (Annoyed Grunt)-Bot". Both pets have had starring roles in several episodes.
The show includes an array of quirky supporting characters: co-workers, teachers, family friends, extended relatives, townspeople and local celebrities. The creators originally intended many of these characters as one-time jokes or for fulfilling needed functions in the town. A number of them have gained expanded roles and subsequently starred in their own episodes. According to Matt Groening, the show adopted the concept of a large supporting cast from the comedy show SCTV.
Despite the depiction of yearly milestones such as holidays or birthdays passing, the characters do not age between episodes (either physically or in stated age), and generally appear just as they did when the series began. The series uses a floating timeline in which episodes generally take place in the year the episode is produced even though the characters do not age. Flashbacks/forwards do occasionally depict the characters at other points in their lives, with the timeline of these depictions also generally floating relative to the year the episode is produced.