Comedian Jim Gaffigan knows that to stay popular on a national level, he has to cover subjects that everyone understands.

"If someone is paying to see it, they don't want to see jokes about things they don't know about," he said from his home in New York City.

For instance, although he watches "Law & Order" -- or he used to watch it -- he refrains from telling jokes about it because not everyone has seen it.

Which explains why he keeps returning to the topic of food.

"You don't have to explain to people what a Waffle House is. That, and I'm a pig," the 42-year-old comic said.

In some of his shows, Gaffigan even makes jokes about how many jokes he makes about food. But he tries to write about subjects that interest him, and it turns out that what interests him is food.

"As I'm writing this new hour [of material], I'm trying to steer away from it, but it ends up that every other topic that I try to tackle seems to be food. Some of it is in finding things that are universal, and finding things that I'm passionate about, whether it's bacon or ketchup."

He sticks with a subject because he prefers to organize a series of jokes around a single topic. If he starts with one solid joke about, say, a package of ketchup, then he'll try to write a whole group of jokes about ketchup to complement it. That way, he can work in self-contained segments.

"When I go on 'Conan' or I go on 'Letterman,' I like to do five minutes on bacon," he said.

For comedy to be successful, it has to come from a forceful point of view -- no one wants to hear jokes that are indecisive. If he is doing a segment on bowling, say, then he first has to determine whether he loves it or hates it. If necessary to avoid comedic indecision, he takes his own viewpoint and heightens it.

But then he makes comments on his own jokes in what he calls his inner voice, a higher, softer voice that represents the audience's perspective.

"The inner voice is a little bit of the running commentary we all have when we hear ourselves talking. It's a little bit of reading people's faces, because stand-up is very much a conversation."

Gaffigan grew up in Northwest Indiana, near Chicago, the youngest of six siblings. After a year at Purdue University, he headed to Georgetown University in Washington, where he studied finance. The night before he graduated, he told a friend that he secretly wanted to be an actor and a comedian.

He thought that everyone wanted to do that.

Eventually, he worked his way into advertising, where he created a weekly series of print ads for American Express and television campaigns for Hardee's. One commercial for the Frisco Burger featured two people attempting to talk but being interrupted by a foghorn.

Working in advertising "taught me word efficiency and economy, what Mark Twain called the nub of the joke."

"It informed my style in that I write and get to the joke pretty quick. I hit a lot of long singles. I'm not going to hit it out of the park, but hopefully I get on base all the time."

Gaffigan said he always used to be known as an actor who did stand-up comedy, until the success of his last hourlong comedy special on television, "Jim Gaffigan: Beyond the Pale." Now he is known as a comedian who also acts.

His roles on the big screen have been mostly small and comic -- he was the driver the highway patrolmen memorably say "meow" to in "Super Troopers" -- or sometimes more dramatic in smaller, independent films. Most recently, he played a TV announcer, along with Stephen Colbert, in "The Love Guru."

On television, Gaffigan played recurring characters on such shows as "Ed" and "That '70s Show," and was a co-star on "My Boys" and "The Ellen Show." He was also the star of his own short-lived sitcom, "Welcome to New York," in which he played a comedian named Jim Gaffigan from Indiana who moved to New York to perform comedy.

"Welcome to New York" was produced by David Letterman's company, with Letterman picking both the project and Gaffigan to star in it. Gaffigan has appeared on his fellow Indiana native's show almost a dozen times, and he was granted the rare honor of being invited to talk with the host after his very first set.

"Letterman was important for so many different reasons," he said. "One, he was this huge comedic influence on me and I think a generation. . . .

"As a comedian, it quieted the critic in my head: Am I really a comic? I haven't been on Letterman. People were asking, 'If you're a comedian, have [you] been on Letterman or Conan?' It's a stamp of approval."