The very intensity that drives Ben Roethlisberger to make thrilling plays on the football field may also make him more prone to ride a motorcycle sans helmet.

Stunned Steelers fans are shaking their heads at the maddening judgment of the Super Bowl quarterback, whose decision not to wear a helmet cost him dearly in an accident on Monday.

But those exasperated groans overlook the essence of the risk taker -- the person who for better and for worse always goes for the gusto, psychologists say.

"They want an exciting, interesting and thrilling life," said Frank Farley, a Temple University psychologist. "At the end of their lives, they want to say they lived it. ... They tend to be natural-born rule breakers. You can look at these people and say, 'They are stupid.' I might say, 'That is their personality.' "

Dr. Farley has traveled the world to talk to some of the most extreme risk takers of our time, from Mount Everest climbers to NASCAR drivers to the man who crossed the Atlantic Ocean in a tiny sailboat.

He even coined a term to describe them: the Type T personality, with the T signifying "thrill."

Like others interviewed, Dr. Farley said he does not know enough about Mr. Roethlisberger to ascertain how much of risk taker he is.

Mr. Roethlisberger, 24, has vehemently denied he is a risk taker. But risk takers often deny that what they do is risky, Dr. Farley said. They are supremely confident beings who believe their fate is in their own hands.

The job of NFL quarterback is by definition risky and creative.

"There are rules, but as the quarterback, you are in a sense making your own rules," he said. "You live by your decisions, in real time, under the gun. The play starts and everything is moving fast."

Likewise, he said, riding a motorcycle without a helmet is a pure Type T thrill with the adrenaline rush, the open air, the roar of the bike.

Dr. Farley divides risk takers into Type T positives -- inventors, entrepreneurs, explorers -- and Type T negatives -- compulsive gamblers, criminals, people who engage in unsafe sex.

In his view, a multimillion dollar athlete's decision not to wear a helmet is veering into the T negative column.

Often a risk taker has both elements to his personality. Albert Einstein took brilliant risks with his thinking, he said, but on the negative side, had illicit affairs. The late John Belushi was a gifted improvisational comedian, a risky form of comedy, but he abused drugs, a risk that killed him.

Risk-taking tends to peak in people in their late teens through their early 20s.

But is it a cocky young guy thing?

Researchers are divided on this.

Citing the rise of women competing in extreme sports such as snowboarding and skateboarding, Dr. Farley said, "I don't think it is something hard-wired between men and women."

He cites Margaret Mead and Helen Keller as famous female risk takers who were thrilled with the adrenaline rush of their original thinking. Ms. Keller once said, "Life is either a daring adventure or nothing," the Type T mantra.

But Adam Goodie, associate professor of psychology at the University of Georgia, said, "Some people find a thrill in risk itself. It is more of a male thing."

Mortality rates bear that out. Young men 18 to 24 are three times more likely to die than women of the same age, mostly from automobile and motorcycle accidents, suicide and homicide, said Daniel J. Kruger, a research scientist at the University of Michigan's School of Public Health.

Throughout history, young men trying to attract a woman have to compete with each other for social status and resources, he said, so they engage in risky behavior.

"There is some component of guys at the bar, strutting around and getting into fights over women," Dr. Kruger said. "But a lot of it is not conscious. Women find it attractive in a partner, someone who is likely to protect them and provide for them." So men, he said, take risks competing for social status.

There appears to be a link between elevated testosterone levels and risk-taking, he said.

"When men get married, their testosterone levels go down. There is a shift in strategy from settling down and becoming a dad," he said. "But when they become divorced, their testosterone level shoots back up" as they look for a new mate.

Risk takers can be as maddening as they are exciting. Although terrible accidents involving risk takers often lead to calls for more rules, Dr. Farley cautions people not to hem in Type T people too much, lest you kill some of their creative spirit.

"This nation was founded by risk takers," he said. "Ben Franklin didn't wear no freakin' helmet when he rode his horse."