Courtesy Ronald Reagan Library via Wikimedia Commons
Athletes, and boxers, in particular, are notorious for being unable to stay retired. Muhammad Ali was no different. While still holding the heavyweight belt in 1979, Ali retired at age 37. He came back the following year to fight, and lose badly to, Larry Holmes. Despite calls for him to retire for good, Ali, seen here in 1983 with President Ronald Reagan, fought one last time on Dec. 21, 1981, losing a 10-round decision to Trevor Berbick.