Who would've thought that an antisocial, pencil-necked geek would be the hero of one of the nation's top TV comedies? But Sheldon Cooper, as played by Jim Parsons on CBS' "The Big Bang Theory" (8:30 p.m. Mondays), personifies the penultimate nerd.

The guys who create the show wanted a character who's both brilliant and bumbling. "One of the keys to Sheldon is it's like the old saying about the dog walking on his hind feet. It's not how good he does it, it's that he does it at all," says Lee Aronsohn, one of the three executive producers of the show.

"That Sheldon engages other humans is the salient point for me. He tries. I mean, he means well. He just doesn't have the tools for it. And I think what's endearing is that he really is a stranger in a strange land. And he knows his limitations many times and tries to deal with them. The fact that he deals with them very badly is where the comedy comes from."

None of the show's writer-executive producers is a scientist, though Bill Prady worked for a time as a computer programmer and was a partner in a computer software company.

"One of the things from the beginning we wanted — when they talked about their work, we wanted it to be real and accurate," says Prady. "And we do it a couple ways. Sometimes we'll have an idea; we'll have a general sense of the science. And then we have a consultant, who is an astrophysicist at UCLA, David Saltzberg, who works with us.

"We'll say, 'Can we have something about neutrinos here?,' and he'll help us out with it. And, you know, there's some stuff we sort of try to stay current with. But we just want it to sound real and accurate. The nerd references we handle in the writers' room ourselves."

"The characters may be smarter than other people, but I don't know if they're wiser than other people. So I think that's where humor comes from."

Chuck Lorre, who created the show with Prady, says, "We try and make the jokes work so that even if you don't understand — obviously the science has to be almost irrelevant. You have to understand the intent that the characters are trying to get across.

"So whether or not you're an astrophysicist ... we try to make the material work without having to understand the science," says Lorre, who also created and runs "Two and a Half Men" with Aronsohn.

"The most fun is when we sit in the room and we try and write the physics stuff ourselves. And Bill will say, 'Chuck, we can sit here forever. You're not going to become a physicist.' "

Physicists or not, the three show runners know a funny line when they hear one. But they're not always on target, says Lorre. Since they shoot in front of a live audience, they know immediately when they've slipped. "Kunal did something. It was last season. It was a disaster. You could hear your career going by. It was awful. It was so quiet the audience took back laughs from earlier in the evening."

When that happens, they will rewrite the joke on the spot until it spawns a laugh. They keep the show from stagnating by illuminating the characters, says Lorre, who's worked on several sitcoms including "Cybill," "Roseanne" and "Dharma & Greg."

"The magic trick of doing a TV series is growing the series, growing the characters without fundamentally changing them. I mean, obviously Archie Bunker has to stay Archie Bunker as the series goes along, but there has to be some incremental growth; otherwise, it gets redundant pretty quickly," he says.

"We have an amazing ensemble on 'The Big Bang Theory.' And we get to do, whatever, 23, 24 shows a year. It is an opportunity to learn more about them and get more depth to them. I think that's something we try to do in learning about where Sheldon and Leonard come from by meeting their mothers. You know, they come from very, very different backgrounds. And that's our attempt at also getting deeper into the characters."