Former undisputed world heavyweight champion Evander Holyfield has revealed that he is coming out of retirement at the age of 57 in order to help raise money for charity. The American isn’t the first sports star to be drawn back into competing, and probably won’t be the last! Some did it because they were bored, others because they missed the competition, others, well, because they missed the money! We’ve taken a look back at some of the greatest athletes who have unretired and made comebacks to professional sport.