If not for the headaches, Joe Rogan might not be a stand-up comedian today. When he was 13, he began practicing martial arts; by 19, he was a black-belt taekwondo champion, winning national and Massachusetts championships for years. But by the late '80s, he'd lie in bed at night after a long day of fighting and feel the pain. "I was really worried about head trauma. I realized 'I'm damaging my brain' at night," recalls Rogan, 38, by phone from Los Angeles. "This is not as simple as paying a game of basketball — 'oh, you got scored on' — this could compromise my ability to think. It really scared me."

Convinced he was on the road to brain damage, Rogan made a shift. One of his best friends, a doctor, declared him funny and suggested he transform into a comedian. Rogan was dubious. "I don't think I'm funny," he said. "I'm funny to my friends. You think I'm funny. Other people think I'm an (expletive)." But the friend persisted, and Rogan found himself at an open-microphone night, where he gathered his courage and went on stage

"Then, off to the races," he says. "I did both for a while. I did three kick-boxing fights while doing stand-up comedy. I realized I wasn't as committed to (martial arts) as I was before."

Today, the fast-talking Boston native is a sort of regular-guy renaissance man. With his high-profile hosting of NBC's smash "Fear Factor" long behind him, he's free to focus on stand-up, with a little podcasting, a little science journalism (as host of SyFy's "Joe Rogan Questions Everything") and a little Ultimate Fighting Championship commentary on the side. Like many veteran comedians, from Jerry Seinfeld to Sandra Bernhard, he's taking advantage of every possible channel that suits him, on TV and online.

But when he first shifted from mixed martial arts to comedy roughly 20 years ago, the brashly confident Rogan wasn't sure if he was doing the right thing. His parents were confused. He hadn't told them about the headaches. ("I didn't talk to anybody about that -- not my trainers, not the people I was competing with," he recalls. "I suspect everybody was sort of keeping it to themselves.") "What?" was his mother's reaction to the news that he was abandoning his passion for an uncertain comedy career. "That seems like a hard thing to do. You don't seem like you're very funny. You're kind of crazy."

Recalling those early days on stage, beginning with Stitches, the Boston comedy club that had just opened at the time, Rogan concurs: "Oh yeah, definitely. I was terrible."

Rogan persisted, developing a comic style that wasn't so much jokes as zealously, and usually profanely, rendered stories and observations. His man-amongst-men material is decidedly pro-marijuana, pro-masturbation, anti-religious bigotry and pro-fatherhood. (A characteristic line, from 2008's "Talking Monkeys from Space," about his new daughter: "She drinks breast milk that my girlfriend pumps like a farm animal.") By 1995, he became successful enough to land a memorable role as the deadpan electrician on NBC's "NewsRadio"; when the series ended in 1999, not long after star Phil Hartman died, Rogan began to receive offers for sitcoms with "awful, awful scripts," which he declined.

That's when he took the hosting job for "Fear Factor," a lowest-common-denominator reality show in which guests ate maggots and worms and hung upside-down from giant cranes. "It was an insane amount of money," Rogan says, after years of giving the show its central voice and promoting it on numerous talk shows. "Even grosser than doing 'Fear Factor' was doing a sitcom that's terrible. I had friends who were doing those. It's brutal."

Today, Rogan picks jobs he truly finds interesting, like "Joe Rogan Questions Everything," in which he interviews scientists and experts about unexplained phenomena, from Bigfoot to chemtrails. And he's as enthusiastic about Ultimate Fighting Championship as he was about "Fear Factor," even as he acknowledges, from personal experience and his own hours of observation, how dangerous it is to fighters' brains. He's walking a fine line — he'll host a show that celebrates the UFC's top kick-to-the-head knockouts, then he'll do a podcast with a doctor specializing in traumatic brain injuries.

"It doesn't mean anything when I say it — until someone comes around and makes some sort of a standard, like when a fighter has had more than 500 impacts to the head, over the course of a measure career, we make them retire," he says. "It's imperative we have these discussions, and fighters realize it's probably safe to compete — up to a certain point."

Between Bigfoot, UFC, stand-up and his family, the post-"Fear Factor" Rogan is living a life of passion rather than a life of drudgery-for-cash. "Fortunately, everything I'm doing, I actually enjoy," he says. "Those things are a part of me — things I like to do in life. It's not unusual to have varied interests. It's just unusual to have a varied career. I guess."

onthetown@tribune.com

Twitter @chitribent

When: 8 p.m. Friday

Where: Chicago Theatre, 175 N. State St.

Tickets: $35-$50; 312-462-6300 or thechicagotheatre.com