Mary Terstegge Meagher Plant (born October 27, 1964) is an American former competition swimmer, Olympic champion, and world record-holder. In 1981 she bettered her own existing world records in the 100-meter butterfly (57.93) and 200-meter butterfly (2:05.96). These times that would stand as the respective world records for 18 and 19 years, and are considered to be among the greatest sports performances ever.
Meagher is the daughter of two-time Notre Dame basketball letterman James L. Meagher. She was a competitive athlete from an early age. At the 1979 Pan American Games in San Juan, Puerto Rico, she set her first world record—at the age of 14—in the 200-meter butterfly. She graduated from the Sacred Heart Academy high school in Louisville, Kentucky, alongside her sister, future U.S. Representative Anne Northup.
Meagher was expected to compete for medals at the 1980 Summer Olympics in Moscow, Russia. However, Meagher, along with the rest of the United States Olympic team, never got her chance due to the American-led boycott of the Moscow Olympics.
However, in 1981 Meagher gave one of the most memorable performances in competitive swimming at the U.S. Swimming National Championships held in Brown Deer, Wisconsin in 1981. At the meet, Meagher set world records in both the 200-meter and 100-meter butterfly, the two primary distances at which the butterfly is contested in competitive swimming. The times for both records were considered astonishing, especially the record of 57.93 seconds that Meagher set in the 100-meters—a drop of over a second. Both times would stand as the world records for nearly two decades: American swimmer Jenny Thompson lowered the 100-meter record in 1999, while Susie O'Neill of Australia set the record in the 200-meter a year later. Some have argued that Meagher's records in the butterfly were among the most impressive records ever set in sport, let alone swimming, ranking among such noteworthy records as Bob Beamon's long jump world record in 1968. These two swims led Meagher to being named Female World Swimmer of the Year by Swimming World Magazine, which she again won in 1985.
At the 1984 Summer Olympics in Los Angeles, Meagher won gold medals in both the 100-meter and 200-meter butterfly races, along with another gold by swimming the butterfly leg of the women's 4×100-meter medley relay for the winning U.S. team in the event final. Returning to compete at the 1988 Summer Olympics in Seoul, South Korea, Meagher won a bronze medal in the 200-meter butterfly. By the time she left competitive swimming, Meagher had won 24 U.S. national swimming titles.