Donncha O'Callaghan (born 24 March 1979) is a retired Irish rugby union player. He began his career with his home province Munster, spending 17 seasons with the province and winning 5 major trophies, before finishing his career with Worcester Warriors in the English Premiership. Internationally, O'Callaghan represented Ireland and was part of the team that won the Six Nations grand slam in 2009. He also toured with the British and Irish Lions in 2005 and 2009, winning 4 caps, and was invited the play for the Barbarians twice. Throughout his career, O'Callaghan played primarily as a lock, though he occasionally provided cover at blindside flanker.