"It's probably the hardest medal I've ever had to work for," said Hansen, who retired after going medal-less in his individual 2008 Olympic races, then returned early last year. "When I decided to come back and swim, I didn't know what to expect and never really talked about getting on the medal stand or anything like that."
In his two previous Olympics, expectations had led only to disappointment.
Hansen set world records in the 100 and 200 breaststroke in the 2004 Olympic trials, only to come up short at the Athens Games, returning home with 100-meter silver and 200-meter bronze medals.
He didn't qualify for the 2008 Games in the 200, then finished fourth in the 100.
"I was looking at the other end of the pool in Beijing and didn't want to be there any more," Hansen said. "[Sunday], I looked at the other end of the pool and I looked at the guy next to me, who was the Olympic champion, and I said, 'I'm going to beat you.' "
The guy next to him was Kitajima, the two-time defending Olympic champion in both the 100 and 200. Hansen did not realize they would be in adjacent lanes until they lined up to walk out for the start. They shook hands.
"I think we both knew what was about to go down. I turned at the 50[-meter mark], and I saw I was ahead of him," Hansen said. "I thought he was the guy to beat in the race, to be honest, so I was like, 'I'm in this thing.' "
Hansen, 30, conjured his trademark finishing speed, climbing from sixth at the turn to the Olympic podium. He finished in 59.49 seconds.
South Africa's Cameron van der Burgh won in a world-record 58.46 seconds, followed by Australia's Christian Sprenger in 58.93. Kitajima was fifth, in 59.53.
"These guys, growing up, they were my idols," the 24-year-old van der Burgh said of Hansen and Kitajima. "It's the proudest day of my life."
Hansen had squeaked into the final, qualifying eighth. He and his coach, Eddie Reese, worked on tweaking his stroke overnight.
"Normally, you don't say something once you get in the semifinals," Reese said. "We knew if we didn't, he didn't have a chance. And a real credit to him that he was able to fix it."
Reese said it was nice to finally see Hansen happy after an individual Olympic race.
"This is probably my favorite medal I've ever gotten in the Olympics," Hansen said.