Wladimir Klitschko is a boxer.
Wladimir Wladimirowitsch Klitschko ( Володи́мир Володи́мирович Кличко́ , ; born 25 March 1976 ) is a Ukrainian professional boxer . Overall , he became the second-longest reigning heavyweight champion of all time , and has the second-most successful title defenses total of any heavyweight boxer with 23 ( including his initial reign as WBO champion ) , behind Joe Louis ( 25 ) and ahead of Larry Holmes ( 20 ) and Muhammad Ali ( 19 ) .