Daniel Steven Kowalski (born 2 July 1975) is an Australian former middle- and long-distance swimmer specialising in freestyle events. He competed in the Olympic Games in 200 m, 400 m and 1,500 m individual freestyle events and in the 4x200 m freestyle relay. At the 1996 Summer Olympics, he was the first man in 92 years to earn medals in all of the 200 m, 400 m and 1500 m freestyle events. Kowalski was however perhaps best known for being perpetual "groomsman" to fellow Australians Kieren Perkins and Grant Hackett, who were respectively the world's best 1500 m freestyle competitors during the earlier and later parts of Kowalski's career. He was an Australian Institute of Sport scholarship holder.
Kowalski was part of the world record setting Australian gold medal 4x200 m relay team at the 1998 Commonwealth Games. Kowalski also holds 400 freestyle long course masters world record in the 30 to 34 age group which he set on 2 May 2009 in a time of 3:58.42.
Kowalski announced his retirement from competitive swimming on 8 May 2002. He studied sports marketing at Bond University, graduating in 2003. He was named as an assistant swimming coach at the University of Wisconsin–Madison in 2007, and also won the 2007 Pier to Pub 1.2 km open water swim held annually in Lorne, Australia.
In February 2004, he was the host of an overnight program on SEN 1116 with former Orlando Magic basketballer Andrew Parkinson. In May 2007 Kowalski appeared as one of the celebrity performers on the celebrity reality singing competition It Takes Two.
In April 2010 Kowalski announced that he is gay. Kowalski says he was inspired to come out by Welsh rugby player Gareth Thomas, who announced the previous December that he was gay. He said "I felt really compelled to do it because it's very tough to live a closeted existence".
In 2010, Kowalski was selected by readers of samesame.com.au as one of the 25 most influential gay Australians.