Feb. 14, 2011 -- The first time "Jeopardy!" champion Ken Jennings went on the popular game show, the ultimate prize was millions in cash. But when he faces off against IBM's super computer Watson this week, he's not just playing for money -- he's playing for all of mankind.
For the past four years, top artificial intelligence researchers at IBM have been preparing their mega-machine, Watson, to compete on "Jeopardy!" against all-time champions Jennings and Brad Rutter.
To win, the machine needs not just to know the facts, but to replicate a human's understanding of all the puns and wordplay woven into the game -- and then be the first to the buzzer.
This week, the much-hyped man vs. machine match-up airs on national television. And, Jennings said, the pressure is on.
"One of the first things I thought was, 'This time, I'm not just playing to pay my mortgage or something, or to feed my kid's college fund, I'm actually sort of representing 7 billion human beings against our new machine tyrants,'" he quipped. "That was a lot of responsibility. I didn't want to let people down."
When "Jeopardy!" first called him a couple of years ago to let him know that IBM was working on a supreme game-show machine, Jennings said he was "skeptical."
As a former computer programmer himself, he said, he knew the computer's limitations and doubted if IBM actually could pull it off.
Humans Can't Match 'Precision' of Watson's Reflexes, Jennings Said
But when he watched taped matches of Watson playing against top human contestants, he realized that beating the computer was hardly a foregone conclusion.
"Clearly, it was playing at a very high level. It sort of effortlessly handled the kinds of things I thought computers couldn't do," he said. "It could understand wordplay, it could understand things that were more conceptual than a single fact."
The three-day match, which airs tonight, Tuesday and Wednesday, was taped in January. Jennings can't reveal the winner, but said this: In speed, at least, Watson takes the top prize.
"Obviously, humans can't duplicate the precision of Watson's reflexes," he said. "If all three players are buzzing, it's going to be Watson because we just can't match its reflexes with our goopy neurons."
Watson Still Has 'Train Wreck' Categories
But when the machine gets something wrong, Jennings said, "it gets it spectacularly wrong."
For example, Jennings said an IBM developer told him that when asked for the Russian word for "goodbye," Watson gave the answer "cholesterol."
"To me, that's just crazy," he said. "There's no way a human player could duplicate that kind of mistake, but Watson has no idea. It just doesn't have all the checks and balances we do."
It wasn't until he saw the machine in action that Jennings also realized that Watson isn't as good at short clues, as it gets less time to think.
And then there are the so-called "train wreck" categories, he said.
"One of the developers was telling me that it'll have streaks of just terrible luck. ... [In] a category that has some angle that it's not getting, it still does fail pretty spectacularly," Jennings said, adding that in a practice session, children's book titles proved especially difficult for Watson.
Jennings: No 'Survivor Guilt' in This Match
But, one thing's for sure, when you're playing against a machine, there's no remorse when it can't keep up.
"I did sort of feel that survivor guilt in 2004, like every time I win a game, it's because I've crushed two other players' dreams," he said. "Playing against Watson ... it really was devoid of that, it could be this killer instinct. I hate this competitor as I have hated no other competitor because ... it has no feelings."
The record-holding "Jeopardy!" winner added that it was nice to be the underdog for a change.
"I got the feeling the first time I was on 'Jeopardy!' that probably, at some point, people were rooting for me to lose, because no one cheers for the Yankees," he said. "And I sort of liked the idea that, this time, presumably everyone except for IBM shareholders is going to be cheering for me and Brad. That was a very good feeling."
Still, Rutter said, those shareholders do have a mighty powerful computer on their side.
"I think humans will be surprised," he told ABCNews.com. "Especially because it's just "Jeopardy!" clues like you see every day on the show. To see a computer actually figuring it out, with all the little twists and turns and puns that they like to get in there, even factoring those in. To see how well Watson is doing, I think might scare some people."
Rutter: Humanity Wins Even If Man Loses
Potentially anticipating the sci-fi-fueled "eventual robot takeover of society," Rutter said IBM has been emphasizing that Watson is an "it" and not a "he."
"I think they sense that people will get freaked out by how well it's doing and how well it can approximate a human," he said.
But regardless of whether Rutter, Jennings or Watson wins the match, Rutter said, no one really loses.
"Ken and I are representing humanity in this thing but, at the same time, Watson was developed, built, programmed by human beings," said Rutter. "So I think humanity wins no matter what happens."
And beyond even that, Jennings said that playing the world's most sophisticated computer gave him a new appreciation for the humble human brain.
"I was impressed at the end that the human brain -- just a few dollars worth of water and salt and protein and whatever else we have in our skulls -- that that could hang in there and play at the same level as this jillion-dollar computer the size of a room," he said. "It says a lot for the human brain that with what we have we can hang with the world's most powerful computer. It's sort of a newfound respect for what our heads can do, which we take for granted sometimes."