The Simpsons are the brainchild of Matt Groening. He started out as a cartoonist by drawing a weekly comic strip for a set of regional newspapers, called "Life In Hell." They featured a rabbit called Binky and detailed the dark side of life. Books of these early cartoons are sold in bookstores.
Then one day, Matt got a call from James L Brooks (now co-producer of The Simpsons). James had seen his comic strip and wanted Matt to do some animation for the Tracey Ullman show - minute long "buffer" cartoons, showing before and after commercials.
Matt originally planned to use his Life In Hell characters, however, at the last moment, he realized that doing this would ruin the characters, so he made up some more characters on the spot: The Simpsons. As he was not feeling particularly creative that day, he named them after his only father: Matt's father is called Homer, and his mother is called Margaret (he thought Marge was a funnier name). He also has two sisters called Lisa and Maggie. He called the main character Bart, because it is an anagram of 'brat'.
The animation and voices of the characters were extremely crappy in comparison with more current Simpsons episodes: "I gave the animators my rough sketches... I thought they were going to clean them up a little, but it turns out all they were doing was tracing my drawings." -- Matt.
The shorts were a big hit, and in 1989 Fox commissioned a whole series: 13 full-length episodes. The animation was still a little crude, but the show was a huge hit nonetheless.
In the beginning, Bart was made to be the main character. This is evident from the vast number of Bart-orientated episodes in the first few Seasons, such as Bart The General and Bart The Daredevil. Bart was also the center of much of the merchandise, and even the focal point of two music videos: Do The Bartman and Trouble.
However, after a few Seasons, it emerged that Homer was more popular, hence the large increase in Homer-orientated episodes in later Seasons, such as Homer The Heretic and Homer Vs. Patty & Selma to name just two.
Nowadays, episodes are not just based around The Simpson family. Episodes featuring supporting characters are very common, such as Hurricane Neddy (Ned Flanders), Worst Episode Ever (Comic Book Guy), and 22 Short Films About Springfield (a host of supporting characters).
The Simpsons has been on our screens for more than 20 years, and still remains one of the best programmes on television.