Riess' parents say that like many poker players, their son always had a head for numbers. As a 14-year-old, he became obsessed with poker after watching amateur Chris Moneymaker win the main event.
"In my basement, I had a $10 home game that I ran twice a week, just playing with my friends. I won all the time, which I thought was kind of weird, so I thought maybe I should do this more often," he said, sipping beer from a can moments after his win.
As soon as he turned 18, Riess began playing in charity poker rooms around his hometown of Watertown, Mich., outside of Lansing, and got a job as a dealer.
Lydia Mobley, who worked alongside Riess at Card Shark's, said she saw him outgrow his early, overly aggressive style and learn how to work a table.
"He was all about power poker; now he's much more relaxed. He's grown so much, by leaps and bounds," she said.
On Monday and Tuesday, Riess made small bets and raises to take down big pots when opponents didn't seem interested in sparring. It was only in the final hour or so that he introduced a more aggressive style to drive his last opponent, Las Vegas club promoter Jay Farber, out of the game.
After hours of scowling and fidgeting with his chips, Riess's boyish face broke into transparent emotion when he won the right to put his name alongside former champions including Doyle Brunson, Phil Hellmuth and Johnny Chan. He choked up as he thanked his friends and family for their support. He said he had no plans for his $8.4 million in winnings beyond a night of celebration.
Riess' fans chanted "Riess the beast" through two days of final table play, talked down his opponent's panda mascot, and then piled on top of him the instant Riess won the championship. But he may not have needed the confidence boost.
Riess has always been single-minded about becoming the world's best poker player, and has been traveling and playing in tournaments at a frenetic pace since graduating from Michigan State University in December, according to friend Jimmy Clifford.
"All of us are like extremely competitive. And we all do something different. Ryan's was poker," Clifford said.
Ever since the final table was set during seven days of play in July, Riess has maintained that he was the best player of the nine finalists. After he won, he told reporters he was the best player in the world.
Girlfriend Tabitha Trask, who has been friends with Riess since the sixth grade, said Riess' confidence won over friends and family who were initially skeptical about his career choices.
"He had so much confidence in himself that I really thought he was going to win," she said. "And he was not nervous today; he was so composed."
Riess' parents figure their recent grad has plenty of time to settle down and find another kind of goal, if that's what he wants. On Tuesday, they were basking in the glory of the win as much as Riess or any of his dozens of increasingly inebriated fans. Unlike their son, they never expected this moment to come.
"He used to have friends come over and play in our basement, or play during the first hour in school. We never imagined he'd make it here. It's just incredible," his mother, Cheryl Riess, said.