Susan O'Neill, OAM (born 2 August 1973) is an Australian former competitive swimmer from Brisbane, Queensland, nicknamed "Madame Butterfly". She achieved eight Olympic Games medals during her swimming career.
Susan (Susie) O'Neill was born on 2 August 1973 in Mackay, Queensland to mother, Trish and father, John. She has two siblings, a brother and a sister. Her family moved to Brisbane and she was educated at Lourdes Hill College (LHC) in Hawthorne. Whilst at LHC, O'Neill excelled in sport, setting school records in 50 m and 100 m butterfly, freestyle, and backstroke. She was also LHC cross country champion and set records for the 13 years 800 m in 1986 and for the 15 years 400 m in 1988 for athletics. All these records still stood as of 2011.
O'Neill won the 200 m butterfly at the 1996 Summer Olympics and the 200 m freestyle at the 2000 Summer Olympics. She won 35 Australian titles and holds the Australian women's record for the most Olympic medals (eight), with Dawn Fraser, Leisel Jones and Petria Thomas.
After winning a gold and a silver medal in her first attendance at a competition at the 1990 Commonwealth Games, O'Neill never failed to win a medal at any international meet she attended, right up until her final Olympics in front of a home crowd in Australia. At the Sydney 2000 Olympic Games Trials, she broke the 19-year-old world record of another "Madame Butterfly", Mary T. Meagher, in the 200m butterfly, but was beaten at the Sydney 2000 Olympic Games by American Misty Hyman, in an upset.
She trained under Bernie Wakefield until 1994, then Scott Volkers at the Commercial Swimming Club in Brisbane.
O'Neill is an ambassador for the Fred Hollows Foundation. She is also ambassador for companies such as SAAB and Kellogg's, and has her own line of swimsuits that is sold in Target stores throughout Australia.