Gregory "Greg" Jagenburg (born c. 1957) is an American former competition swimmer and a World Aquatics Champion in butterfly who swam for Long Beach State and the University of Arizona under Hall of Fame Coach Dick Jochums.

In August 1975, Jagenburg swam a 2:00.73 in the 200-meter butterfly, just .03 seconds behind Mark Spitz's standing world record in the 1972 Munich Olympic Games.

[2] Three years later, around May, 1978, at the US-USSR dual meet in Austin, Texas, Jagenburg would become one of three swimmers to break Spitz's 1972 Olympic world record of 55.7 seconds in the 100-meter butterfly.

[20][21][22][23] At Long Beach State, near Los Angeles, he studied theatre arts and may have been influenced by his mother Ellen Dunlop who was an actress and singer on Broadway.

[24][25] As an upperclassman, Jagenburg transferred to the University of Arizona to swim with his former Long Beach State Coach Dick Jochums along with Long Beach State backstroke swimmers Olympian Tim Shaw and Bob Jackson, who lent considerable ability to a formerly struggling program that had recruited other top swimmers that year and anticipated a much better season.

Jochums, realizing the strength of his team, set his goals on the NCAA championships and the Olympic trials rather than focusing exclusively on Dual Meets.

[26][27] Swimming for Arizona at the March 1980 NCAA Championships in Cambridge, Massachusetts, Jagenburg slipped to seventh place in the 100 butterfly with a 48.91 against stiffer competition who could shave seconds off his personal best times.