Perhaps the most famous example is that of George Foreman, who won the WBA, IBF, and lineal heavyweight titles by knockout over Michael Moorer in 1994 at the age of 45. He would successfully defend that title four more times, through the age of 48. That made Foreman the oldest major title holder ever – a record that lasted until Bernard Hopkins won the WBC light heavyweight title in May 2011 at age 46.
