Nathan Ghar-jun Adrian (born December 7, 1988) is an American competitive swimmer and five-time Olympic gold medalist who formerly held the American record in the long course 50-meter freestyle event.

In his Olympic debut at the 2008 Summer Olympics, Adrian swam in the heats of the 4×100-meter freestyle relay and earned a gold medal when the United States team won in the final. At the 2012 Summer Olympics, Adrian won gold medals in both the 100-meter freestyle and the 4×100-meter medley relay, and a silver medal in the 4×100-meter freestyle relay. He has won thirty-two medals in major international competitions; twenty gold, seven silver, and five bronze in such competitions as the Summer Olympics, the FINA World Aquatics Championships, and the Pan Pacific Swimming Championships. In the 2016 Summer Olympics 4x100-meter freestyle relay a gold was won with Michael Phelps, Caeleb Dressel, and Ryan Held. He was an individual bronze medalist in the 50-meter and 100-meter freestyles.

Adrian was born in Bremerton, Washington, in 1988. He is the son of Cecilia and James Adrian. His mother is Chinese from Hong Kong and works as a nurse for the Bremerton school district; his father is a retired nuclear engineer for the Puget Sound Naval Shipyard. Adrian has an older sister, Donella, who swam at Arizona State University, and an older brother, Justin, who swam at the University of Washington. Adrian started swimming at the age of five because of the influence of his siblings. He graduated in 2006 from Bremerton High School, where he swam for the school team.

Adrian attended the University of California, Berkeley in fall 2006, where he majored in public health and competed in swimming under Head Coach Dave Durden. He graduated with honors in the spring of 2012. Adrian was a five-time individual NCAA champion, winning the 50-yard freestyle in 2009 and 2011 and the 100-yard freestyle in 2009, 2010, and 2011.

At the 2008 Short Course World Championships, Adrian won gold in the 100-meter freestyle and 4×100-meter freestyle relay and silver in the 4×100-meter medley relay. In the 4×100-meter freestyle relay, Adrian combined with Ryan Lochte, Bryan Lundquist and Doug Van Wie won gold in a world record time of 3:08.44. In his second event, the 100-meter freestyle, Adrian won gold in a time of 46.67, just ahead of Filippo Magnini who finished second with a time of 46.70. For his last event, the 4×100-meter medley relay, Adrian combined with Randall Bal, Mark Gangloff and Ryan Lochte, won silver behind Russia.

At the 2008 United States Olympic Trials, Adrian placed fourth in the 100-meter freestyle, qualifying him to swim in the 4×100-meter freestyle relay at the Olympics. He also placed sixth in the 50-meter freestyle.

At the 2008 Summer Olympics in Beijing, Adrian swam the first leg in the preliminary heats of the 4×100-meter freestyle relay, splitting a time of 48.82 seconds. Cullen Jones, Ben Wildman-Tobriner and Matt Grevers completed the relay with a final time of 3:12.23, a world record. This record was broken one day later when Michael Phelps, Garrett Weber-Gale, Cullen Jones and Jason Lezak swam a time of 3:08.24, beating France and Australia in the final. By swimming in the heats, Adrian earned a gold medal even though he didn't swim in the final.

Adrian was training under coach Mike Bottom in the Florida Keys as part of The Race Club swimming training program World Team leading up to the 2008 Olympics.