A curious mind, good memory and astute buzzer technique, said Jennings, a Utah software engineer who will make an unprecedented 29th appearance on the syndicated quiz show Monday night.
"A lot of it is just God-given memory that I can't take any credit for," he said. "I've always been interested in a lot of different fields. It's not just that I'm a computer engineer and all I care about is computers."
Playing "Jeopardy!" fulfills a longtime dream, said Jennings, 30, although he concedes the cash prize is a bit dreamy, too.
"It's enough fun that the money's just icing on the cake," he told The Associated Press. "But there seems to be a lot of icing."
There's also an unexpected measure of celebrity. A few "Jeopardy!" champs have caught the public eye — such as New York City transit cop Frank Spangenberg with his then-record $100,000-plus winnings in 1990 — but it's typically the challenging game itself that's the star.
Jennings' run that started airing June 2 has changed that, especially as he nears $1 million. On Monday, he's set to appear on ABC's "Good Morning America" and on CBS' "Late Show with David Letterman."
Jennings admits feeling nervous and a bit overwhelmed by the attention.
"I remember the first time I was watching Diane Sawyer mention me," Jennings said. "Suddenly hearing her say, 'Ken Jennings,' it was very surreal. It's a little weird to me I get recognized in the grocery store, and Letterman's calling."
Not bad for a family man who gives a self-deprecating shake of the head when his cash total is announced and whose boldest gesture is adding a flourish to his name on the player ID screen.
Jennings is making the most of a change in "Jeopardy!" rules. To mark the start of its 20th season last September, the quiz show lifted its five-game limit for winners and allowed them to keep going until they lose.
On the show, which is taped in advance and crams five shows (a week's worth) into one day of production, players are given answers in a wide variety of categories and must quickly buzz in to pose the correct question.
"I admire the heck out of the guy," said Bob Harris of Los Angeles, a "Jeopardy!" five-time champion who competed before the rule change. "To run five games straight any day is mentally exhausting, and he does it flawlessly, with a big smile on his face."
"I'd be lying if I said there wasn't a certain degree of envy," added Harris, a political satirist who writes for TV and film.
Previous record-holder Tom Walsh, 39, of Washington, D.C., managed a seven-day run with $184,900 in winnings on the show in January.
A Seattle native who grew up in South Korea — his father works for an international law firm in Seoul — Jennings watched "Jeopardy!" on the U.S. Armed Forces TV network and thought to himself, "Hey, maybe you could go on 'Jeopardy!'. You're not half bad at it."
After years of toying with the idea, he finally got "fed up with being wishy-washy," he said, and made a road trip to Los Angeles to audition. When he was invited on the show, friends and family predicted big things.
A member of Brigham Young University's College Bowl team in the 1990s, Jennings writes and edits literature questions for the National Academic Quiz Tournament.
He insists he had modest hopes, knowing full well how tough the "Jeopardy!" competition can be.
"My expectations were maybe to get a few answers to show I wasn't a total dummy, so even if I was getting shut out on the buzzer I still looked like I knew a thing or two," he said. "And I would have been happy with that."
His love of novels — he was an English literature major in college — and general fascination with the world have served him well on "Jeopardy!"
He's also got a willingness to study. A teetotaler, Jennings read up on alcoholic drinks in anticipation of the "potent potables" category that can, and did, come up. He's easily handled it.
He has one regret: a "vague collective guilt" for the players who had the misfortune to come up against him as he's become increasingly comfortable on the show.
Jennings expects to invest what he's won for wife Mindy and their 1 1/2-year-old son, Dylan. There will be a splurge or two, probably on a trip to Europe.
The movie buff managed to come up with wrong answer to that question the first time his wife raised it.
"She asked me what we're going to do with all the money and I told her it's all going to DVDs. I don't think she thought that was too funny," Jennings said.