Gary Steven Ilman (born August 13, 1943) is an American former competition swimmer, two-time Olympic gold medalist, and former world record-holder in two relay events.
Ilman made his international swimming debut as a member of the U.S. national swimming team at the 1963 Pan American Games in São Paulo, Brazil. He was a member of the U.S. squad that won the gold medal in the men's 4×200-metre freestyle relay, together with his American teammates Richard McDonough, David Lyons and Ed Townsend.
Ilman represented the United States at the 1964 Summer Olympics in Tokyo, Japan, where he won gold medals as a member of the first-place U.S. teams in the men's 4×100-meter freestyle relay and men's 4×200-meter freestyle relay. In both freestyle relay events, Ilman and his American teammates broke existing world records. Steve Clark, Mike Austin, Ilman and Don Schollander set a new world record of 3:33.2 in the 4×100; then Clark, Roy Saari, Ilman and Schollander set a new world mark of 7:52.1 in the 4×200.
In individual competition, he finished fourth in the 400-metre freestyle event final. In a controversial outcome, both Ilman and German swimmer Hans-Joachim Klein were officially timed at 54.0 seconds (to 1/10 of a second), and were still tied at 54.00 (to 1/100 of a second) using the new unofficial electronic timing, but the judges on their own initiative awarded the bronze medal solely to Klein on the basis of the unofficial electronic time taken to 1/1,000 of a second.
Ilman finished his international swimming career at the 1965 World University Games in Budapest, Hungary, where he won a pair of gold medals as a member of the winning U.S. relay teams in the 4×100-metre and 4×200-metre freestyle relay events, and a bronze medal in the 100-metre freestyle.