By now, a generation of TV viewers takes this for granted: Most Sundays nights, Fox has cartoons for grown-ups. And around Halloween, it has "Treehouse of Horror."

Now "Treehouse" is back. It "airs Nov. 2, which is when we celebrate Halloween in our house," jokes producer Al Jean.

That slight delay is due to the World Series. When "Treehouse" arrives, it dares to give "It's the Great Pumpkin, Charlie Brown" a dark twist.

"The Great Pumpkin comes to life, and he's so upset at what humans do to pumpkins that he tries to kill and eat everybody," Jean says.

Hey, that sort of thing happens in "Treehouse." Since these are just tales, anything is possible. This time, Homer kills celebrities; also, he ends up as a piece of a giant foosball game. All of that is part of a TV tradition. People might forget how unique such shows were.

"Everyone in the dorms would get together to watch 'The Simpsons,' " recalls Mike Barker, now an "American Dad" producer. "It was a form of community."

It was also just about the only TV show he watched. When a friend, Matt Weitzman, asked him to co-write a TV script on speculation, Barker says:

"I basically admitted, 'I don't watch a lot of television, so I don't think I'm going to be very useful to you.'

"And he's like, 'Well, what if we wrote a 'Simpsons'?"

They did, and got work. After writing regular situation comedies for a while, they've spent the past eight years doing "Family Guy," "Father of the Pride" and "American Dad."

That's typical, says producer Seth MacFarlane. "The Simpsons" was a starting point for most of TV's cartoon people.

"It's so rare that something comes along that you see, and it just completely catches you off-guard," MacFarlane said.

At the Rhode Island School of Design, he aspired to mainstream animation — until "The Simpsons" arrived. "I said, 'I don't want to work for Disney. I want to do that.' "

Some such fans now work for "The Simpsons," says Matt Groening, the show's creator.

"We do have writers who have grown up watching the show. ... They have the show memorized, and they've watched every episode."

And others branch out, creating their own. After working briefly for the Cartoon Network and Disney, MacFarlane became a Fox factory.

He created "Family Guy" in 1999 and "American Dad" in 2005. They joined a universe that included "The Simpsons" (1989) and "King of the Hill" (1995).

"They both had this very kind of underground look," MacFarlane says. "They didn't look that slick. ... That told you this is not a kids' show."

That's still a goal, Groening says, despite a change in technique. "It's drawn by hand, (but) inked and painted on computer. ... We dirty up the picture, ... so it doesn't look like it's done by computer."

These shows make stars of their voice actors. Pamela Adlon is an on-camera actress, a regular in "Californication" and (recently) "Lucky Louie," but that's not her main occupation.

"Even when I go to my kids' career day, I always write 'voice actor,' " she says.

Then the kids learn that their classmate's mom plays Bobby Hill. "He's sweet and he's funny," Adlon says of Bobby.

And he's part of a TV tradition, taping more than 250 "King of the Hill" episodes so far. Created as a "Simpsons" companion piece, the show is part of an animation avalanche.

For now, Fox has quit mixing in some noncartoons.

"Your brain adjusts to a certain pace in that first half-hour," MacFarlane says. "I think if you put an episode of 'Seinfeld' on after an episode of 'The Simpsons,' 'Seinfeld' would feel slow and sluggish."