At six-foot-five, the Frenchman has used his extra-long frame to dominate on consecutive nights in the Olympic pool.
First came his come-from-behind anchor leg to push ahead of Ryan Lochte and the Americans in the 4x100 freestyle relay on Sunday. Then on Monday, Agnel routed a stellar field by nearly two seconds to win the 200 free individual event, earning a congratulatory handshake from French President Francois Hollande.
Agnel led from start to finish and clocked 1 minute, 43.14 seconds for the best time ever in a textile suit, a whopping 0.72 ahead of Michael Phelps' 2007 mark.
Defending silver medallist Park Tae-hwan of South Korea and 400 free champion Sun Yang of China shared silver in 1:44.93, while world champion Lochte finished fourth and world-record holder Paul Biedermann of Germany was fifth.
With so many standouts, and despite Phelps' decision not to enter, the event was dubbed the "Race of the Century."
"I had to look twice at the scoreboard to be sure it was the right time. I had a race plan in my head, but this is above my expectations and hopes," Agnel said. "I worked on keeping my speed and putting all my guts into the last 50. I don't know what to say — it worked."
Afterward, Hollande worked his way past journalists to congratulate Agnel in a media area under the pool.
"Remarkable, two gold medals two nights in a row," Hollande said, dwarfed by the towering Agnel. "It's a big reward for French swimming, a proud moment for him and encouraging for the whole Olympic team."
Camille Muffat gave France another gold in the women's 400 free on Sunday and France stands second to the United States in the swimming medals table.
France had never won more than one gold in the pool at an Olympics, and had a total of three golds before these games: Jean Boiteux won the 400 free at the 1952 Helsinki Games, Laure Manaudou won the 400 free at the 2004 Athens Games and Alain Bernard took the 100 free four years ago in Beijing.
The overflowing success at these games has been a pleasant surprise for a team undergoing a generational change, with Bernard qualifying only for a morning heat in the relay and Fred Bousquet, another sprinting standout, failing to make the team altogether.
Still a baby-faced 20-year-old, Agnel won eight golds at the 2009 and 2010 European junior championships and he is competing in his first Olympics.
He shot to prominence at the senior level two years ago with his victory in the 400 free at the 2010 European Championships in Budapest, although he struggled at last year's worlds in Shanghai with a fifth-place result in the 200.
Named after French tennis great Yannick Noah, Agnel played tennis before he discovered swimming at the age of eight in his neighbour's pool in the southern France town of Nimes.
His parents split when he was 11 and Agnel met his coach Fabrice Pellerin after moving to Nice.
"My parents' divorce was really a tough blow," he said. "But it helped me to grow up, to become more responsible and to be stronger mentally."
Agnel is a shy and discreet guy and doesn't like to go out and party. He does his talking with his swimming.
"He's a great racer, there's no doubt about it," Lochte said. "He's quick and he showed it last night and tonight."
Agnel's next event comes Tuesday morning with the 100 free heats. He's also swimming the 4x200 free relay and the 4x100 medley relay.
"That's going to be complicated," Agnel said of the 100.
The favourites for the 100 are James "The Missile" Magnussen and James "The Rocket" Roberts of Australia plus Cesar Cielo of Brazil, but at this point nobody's counting out Agnel for the sport's signature event.
"As they say in English, 'It's giving me positive vibes,'" Agnel said. "We're on track. We'll approach it without pressure, and with a lot of pleasure and fun, which we've been doing since the start of the week."
AP Sports Writer Samuel Petrequin contributed to this report.