One is 34 years old. The other is a mere 21.
For one, Rio marks his third Olympics. For the other, these Games are his first.
The past, present and future of the U.S. Track and Field program could be distilled to two sprinters competing in the men's 100 meters: Justin Gatlin and Trayvon Bromell.
But after the final Sunday night, neither is the face of track and field.
That title is reserved for Jamaica’s Usain Bolt. Again.
Bolt won his third straight Olympic gold medal in the 100 meters Sunday night, recording a time of 9.81 seconds. Gatlin's time of 9.89 was good enough for silver, and Canada's Ande De Grasse's 9.91 earned bronze.
Bromell finished eighth with a time of 10.06.
Bolt, 29, won gold in the 100 meters, 200 meters and 4x100 meters relay in the 2008 Beijing Games, then again in London in 2012. He comes to Rio as the Olympic Record holder in the 100, which he set with a time of 9.63 in London, and the owner of the World Record, which he set in Berlin in 2009 with a time of 9.58.
Bolt is scheduled to run in the 200 meters and 4x100 meters relay again in Rio.
While Bolt entered the 100 meters as the two-time defending champion, Gatlin came to Rio as a champion on the defensive. Twice suspended for performance-enhancing drug offenses, including a ban that kept him out of the 2008 Beijing Games, Gatlin has gotten an earful of criticism, some from a U.S. teammate.
After winning the women’s 100 meter breaststroke on Aug. 8, swimmer Lilly King of the U.S., who had been outspoken in her criticism of Russian silver medal winner Yulia Efimova’s doping history, was asked about Gatlin and his fellow U.S. sprinter Tyson Gay.
“Do I think people who have been caught for doping offenses should be on the team?” King said. “No, they shouldn’t.”
After recording a time of 10.01 seconds heat on Saturday, Gatlin, the former University of Tennessee Volunteer shot back: “I don't even know who Lillly King is.”
Gatlin believes he’s paid his debt to the sport.
"I've worked hard, all the way from the bottom when I had nothing," Gatlin told the Associated Press earlier. "I worked hard to work back to where I'm at now. I don't understand. The system has worked. I think people need to stop looking at trying to be the judge, the jury and executioner and let the system do its job."
By taking silver, Gatlin joins Bolt as the only two men in Olympic history with three medals in the same discipline. Gatlin won a gold medal in the 100 meters in the 2004 Athens Games. Gatlin also collected a bronze in the 200 meters and silver in the 4x100 relay in Athens, and later added a bronze in the 100 meters in the 2012 Games in London.
It wasn't gold, but it was a strong showing for Gatlin.
Bromell only wishes he could say the same, despite entering the Games excited about his first Olypmic experience.
"This was the dream, to be in the Olympics,” Bromell, a sprinter at Baylor University, told the Tampa Bay Times.
Bromell is the reigning World Champion in the 60 meters, and has a bronze in the 100 meters, earned in the 2015 World Championships. He is also a NCAA All-American in the 100-meter and 200-meters.
“I've already got everything I wanted,” Bromell told The Times. “There are no worries. There's no pressure. Everything else is extra. I can just go and compete and live it out. If I win, then it was meant to happen. It was part of God's plan."
Bromell, a rising senior on Baylor University’s track team, advanced to Sunday’s semis as one of five sprinters to finish with a time of 10.13 seconds. American Marvin Bracy, a member of Florida State University’s football and track teams before forgoing his amateur status to turn pro in track in 2013, also qualified for the semifinals with a time of 10.16.
Prior to the Olympics, Bromell and Gatlin had developed a friendship and working relationship. As NBCBayArea.com reported in July, Gatlin has taken Bromell under his wing.
“A lot of people don’t know how good of a mentor this guy is,” Bromell said of Gatlin.