This week he took his first steps inside the White House, but Barack Obama may soon have a more pressing invitation. An invitation to Springfield, home of the world’s best-loved dysfunctional family.

“We’d love to get Obama,” says Al Jean, head writer and executive producer of The Simpsons. “But he’s kinda busy right now.”

Two days before the US presidential election, an episode of The Simpsons was aired showing Homer’s bungled attempt to vote for Obama. “He used an electronic voting machine but it went wrong and he ended up voting for McCain several times,” says Al. “Thank God that didn’t really happen.”

Created by Matt Groening, with characters named after his family, The Simpsons is the world’s most popular comedy series. A parody of middle-class America, lampooning aspects of the country’s culture and society, it centres on the domestic life of Homer, Marge, Bart, Lisa and Maggie in picket fence-lined Springfield.

Al is a special guest at Bradford Animation Festival, starting today. An Emmy award-winning producer/writer, he’s worked on The Simpsons since the first series in 1989.

He’s currently working on the 20th series and admits that it’s difficult coming up with fresh ideas. This must be particularly stressful when, as is the case with a huge fanbase, there are eagle-eyed obsessives poring over each episode.

“It gets hard maintaining the quality and there is pressure from fans, although that’s not as great as the pressure I feel inside,” says Al. “But it’s still fresh and the ratings are up. Our recent Halloween show was number one in the ratings. Fans keep watching it, I think it has a long way to go.” A Harvard graduate, Al cut his comedy teeth writing for The Lampoon, the university’s long-established humour magazine, and went on to write for Johnny Carson on The Tonight Show, Eighties sitcom ALF, about a cuddly alien living with a suburban family, and stop-motion animation The PJs.

In 1994 Al created The Critic, an animated series voiced by Saturday Night Live comic Jon Lovitz, and he was a producer on the It’s Garry Shandling Show.

Today Al’s name is as synonymous with The Simpsons as Matt Groening and producer James L Brooks. Al, 47, has written countless episodes, including Moaning Lisa, various Treehouse Of Horrors and Hello Gutter, Hello Fadder, and has a prominent input on the DVD commentaries.

Stop-motion animator Barry Purves, also a BAF guest, whose work includes the last King Kong movie and TV’s Postman Pat, told me he feels protective of his puppets to the extent that he won’t leave them lying down after a scene has been shot. Whenever he visits the National Media Museum he visits his creations displayed there, “just to check they’re okay.”

It may be just a puppet animator thing, but I wonder whether Al, who admits to a soft spot for Lisa and Comic Book Guy, feels a fatherly protection towards the characters he writes for in The Simpsons. “It’s more of an uncle thing, since I didn’t create them,” he smiles.

“I’m protective in the sense that I’m careful not to do anything to make people fall out of love with them. That’s been a rule of thumb from the start. This is the greatest show in the world, everyone has affection for these characters and there’s a big responsibility with that.”

The Simpsons started life as crudely-drawn shorts on the Tracy Ullman Show. Was there any inkling of the global phenomenon it would become? “The animation was rougher but it was popular from the start and people took to the characters,” says Al. “I believed in the show because its warmth and relatability was the genius of Jim Brooks. I thought it’d be big, but when you look at how far we’ve come 20 years later – who knew?”

In a world saturated with reality TV, Al has said that The Simpsons is one of the few things left on television that isn’t “a bunch of people trying to have sex on a tropical island.” Is its appeal that it’s essentially an old-fashioned sitcom? “That’s it,” says Al. “This show is about a family and most people can identify with having a family. The characters aren’t perfect, but what family is perfect?

“Writing for animation, the characters don’t age. We’d never do that. It was a deliberate move, and a genius stroke, to create a family of very simple animated characters. Any child can draw The Simpsons. That’s so they stand out against the other characters; you’ll always spot Homer in a Springfield crowd scene. They are unusual yellow figures with an overbite, but people identify with them. A lot of the inspiration came from the Muppets; lots of expression with very little movement.”

The widespread appeal of The Simpsons spans generations of viewers. “Kids and adults enjoy it for different reasons,” says Al. “We write it primarily for adults. We don’t show anything offensive, but we don’t shy away from cultural references that kids won’t understand. There has been an enormous renaissance in animation; Pixar productions like The Incredibles are loved by both adults and kids.”

When The Simpsons began, the production team played down the identities of the voice actors, so the characters could exist in their own world. But today there are regular guest appearances by everyone from Bono to Tony Blair.

“We have great voice actors – that’s always been a strength of the show,” says Al. “I grew up watching cartoons like Bugs Bunny and, for me, the voices were the characters. That’s still the case generally with animation. Nobody watches The Simpsons for the celebrities, but we’re very lucky to get the guests we do. There are some I’ve been thrilled with, like the Beatles. How cool is that? One of our biggest coups was Thomas Pynchon, America’s most reclusive author. In the show he wore a paper bag over his head but it’s his voice.”

He’s not revealing who may crop up in the new series, but could be saving that for Friday’s question-and-answer session. Al is looking forward to his Bradford visit and is excited to hear about original Wallace And Gromit figures on display in the museum. “I’m a big Nick Park fan. I love The Wrong Trousers – it has an element of Buster Keaton,” he says. “I’ve heard great things about your animation festival. We don’t really have those in America, it’s more a European thing.”

Finally, the obvious question, but one most Simpsons fans probably want to know: Is there going to be another movie?

“If we get an idea for a movie that’s good enough, then yes,” says Al. “For now our focus is on finishing this series.”

Al Jean in Conversation is at Pictureville Cinema, the National Media Museum, on Thursday at 2pm.