Mark Daniel Gangloff (born June 8, 1982) is an American former competition swimmer for Auburn University, and was an Olympic gold medalist as a breaststroker in the 4x100 medley relay in both the 2004 Athens and 2008 Beijing Olympics. He is a former world and American record holder, and has coached swimming as an Assistant at Auburn, in age group competition for SwimMAC Carolina, and in the collegiate ranks for the University of Missouri Tigers and the University of North Carolina Tarheels.

Gangloff was born in Buffalo, New York, on June 8, 1982, to parents Ken and Jennifer Gangloff. He attended Akron's Harvey Firestone High School where he swam for Head Coach Tim Lewarchick and Assistant Coach Cindy Dial, graduating in 2000. As a Senior at Firestone, he set an Ohio State meet record time of 1:47.63, while winning the 200-yard individual medley. During his High School career, he was a multi-year All American and won four individual Division I Ohio State Championships, while competing in fourteen events. As a High School Senior in 2000, he swam a state meet record time of 55.10 in the 100-yard breaststroke, and had formerly taken state titles in the 100 breaststroke in both his Sophomore and Junior years.

He accepted an athletic scholarship to attend Auburn University, where he swam for the Auburn Tigers swimming and diving team in NCAA competition under Head Coach David Marsh from 2001 to 2005, serving as a Captain in his senior year.

At Auburn, Gangloff helped the team capture NCAA championships in two seasons from 2003-2004, and take Southeastern Conference titles all four years of his swimming eligibility. He won twelve honors as an All American, and gained individual SEC titles in the 100 and 200 breaststroke and in the medley relays for both the 200 and 400 distance. By his Senior year, he was considered American's third fastest swimmer in the breaststroke. Gangloff graduated from Auburn in 2005 with a bachelor's degree in criminology.

Gangloff represented the United States at two consecutive Summer Olympics winning a gold medal in each. At the 2004 Summer Olympics in Athens, he earned a gold medal by swimming for the winning U.S. team in the preliminary heats of the 4×100-meter medley relay, an event in which the American team had long been dominant. Gangloff swam breaststroke in the second position in the second preliminary heat, which placed first with the team of Lenny Krazelberg, Michael Phelps, and Neil Walker as anchor. The preliminary team swam a 3:35.10, allowing the American team to advance to the finals, where the U.S. team, without Gangloff, later swam a combined time of 3:30.68.

In individual competition, he placed fourth in his signature event, the men's 100-meter breaststroke with a time of 1:01.17, placing him only .29 seconds from medal contention. The Gold, Silver and Bronze medals were won respectively by a Japanese, American and French swimmer. He finished behind the third place French swimmer Hugues Duboscq, who swam a time of 1:00.88 just edging out Gangloff for the bronze.

In international competition, Gangloff swam in three Pan-American Games, taking 400 medley relay golds in 2003 and 2007. He had a first place medal in 2003 in the 100 breaststroke, and in 1999 captured a third place medal in the 200 breaststroke. Between 2005-2011, he was a gold medalist three times at the Long Course World Championships in the 4x100 medley relay in 2005 in Montreal, in 2009 in Rome, and in 2011 in Shanghai. In the Short Course World Championships, he was a gold medalist in the 4x100 medley relay in 2004 in Indianapolis and 2010 in Dubai.

Gangloff swam professionally in 2007, for Mechlinberg Aquatic Center in Charlotte, North Carolina, and swam as a U.S. team member during his career.