What makes Ralph Nader run?

Ralph Nader can still remember his lines from a long-ago appearance on "Sesame Street." "Consumer advocate in the neighborhood," Mr. Nader gently sings over and again in a raspy voice. "I must have been told to say that 200 times to get the right inflection."

Mr. Nader didn't get invited on "Sesame Street" for his deliberate phrasing. The man who once revolutionized car safety has been popping up in some unexpected places ever since he became a national figure.

"Sesame Street." "Saturday Night Live." "Da Ali G Show." "The Simpsons."

The famously ascetic activist has been trading on his renown for decades and getting laughs along the way.

Truth is, he's pretty funny in person. His wit is as dry as a regulatory hearing transcript, but his laugh is a welcoming rumble.

Humor helps spread his advocacy message, and he says his performances have an historical precedent, albeit a thin one.

"In the medieval period, one day a year everybody would dress in costume, whether they were rich or poor," Mr. Nader says. "It was a leveling process."

His method, be it for "SNL" or a cameo in 2005's "Fun with Dick and Jane" remains the same.

"Even though you're acting, you better be yourself," he says. "That's not an easy prescription."

During one "SNL" skit, a toy air bag meant to expand when Mr. Nader bumped into a cast member didn't go off as planned. He speaks of not losing focus with a surprising touch of pride.

He is equally proud of how he uses entertainment to explore themes near and dear to his advocacy heart.

During one "SNL" show, he recalls, "We were able to almost list the things we wanted from the Carter administration."

Mr. Nader doesn't appear in as many entertainment forums as he once did, and anyone who catches the new documentary "An Unreasonable Man" will understand why.

Mr. Nader is the focus of the film, which puts his career — and political aspirations — under the microscope.

We're reminded of his early work to improve car safety and the measures General Motors Corp. took to try to silence him. That included a famously failed seduction.

He credits a strong family for giving him the fortitude to resist such temptations.

"Some people take pressure and rise to the occasion," he says, citing athletic heroes who remain cool during the big game.

"Why should that be restricted to sports?" he asks, laughing.

But the heart of the documentary concerns Mr. Nader's presidential run in 2000 and the radioactive fallout.

Mr. Nader gave interviews to "Unreasonable" filmmakers Henriette Mantel and Steve Skrovan, but otherwise had no direct input into the feature.

Still, the film clearly has two objectives: Pay homage to Mr. Nader's early crusader missions and defend the former Green Party's role in the 2000 election of President George W. Bush.

Mr. Nader would have preferred if the film didn't focus so heavily on the presidential races, but "they were looking for the controversy" he says with a shrug. He is less forgiving about those who share his liberal ideology but won't embrace his third-party measures.

"It's political bigotry," says Mr. Nader, who is mulling another run next year. "Usually, the spokespeople on this side are very analytical. They're writers, accomplished people, but when it comes to analyzing the two-party system with a third party candidate, they can be adolescents."

Whether he runs in 2008 or not, Mr. Nader realizes his entree to the hottest parts of today's pop culture is being curtailed.

"I can't go on MTV," he says. "It's too fast for the human mind to digest ... When you think of how many scene changes a minute, it's totally unbiological."

He wouldn't mind going back on "SNL" for what he says would be his fifth appearance.

Even Mr. Nader knows about the show's "five-timers" club.

He doesn't expect it will happen given the entertainment community's left-leaning ways.

"In 2004, ['SNL' creator] Lorne Michaels didn't invite me on," Mr. Nader says with a laugh. "The attitude even penetrated 'Saturday Night Live.' "