Grant George Hackett OAM (born 9 May 1980) is an Australian swimmer, most famous for winning the men's 1500 metres freestyle race at both the 2000 Summer Olympics in Sydney and the 2004 Summer Olympics in Athens. This achievement has led him to be regarded as one of the greatest distance swimmers in history. He also collected a gold medal in Sydney for swimming in the heats of the 4 × 200 m freestyle relay. He was well regarded for his versatility, and has held the long course world records in the 200 m, 800 m, and 1500 m freestyle events. He dominated the 1500 m event for a decade, being undefeated in the event in finals from 1996 until the 2007 World Aquatics Championships. In total, he has won 10 long-course world championship gold medals.

Hackett was the captain of the Australian swimming team from the time the role was reintroduced in 2005 until his retirement in 2008.

Hackett worked for the Nine Network, often hosting Wide World of Sports. Hackett's contract as a Westpac Banking Corporation ambassador was not renewed in February 2012 after 13 years in the role, but he remains an employee of the organisation. He is currently the Chief Executive Officer of Generation Life.