Wladimir Klitschko, Ukrainian boxer
Wladimir Wladimirowitsch Klitschko (Ukrainian: Володимир Володимирович Кличко, born 25 March 1976) is a Ukrainian former professional boxer who competed from 1996 to 2017. He held the world heavyweight championship twice, including the unified WBA (Super), IBF, WBO, IBO, and Ring magazine titles. A strategic and intelligent boxer, Klitschko is considered to be one of the best heavyweight champions of all time. He was known for his exceptional knockout power, using a strong jab, straight right hand and left hook, quick hand speed, athleticism, as well as great footwork and mobility, unusual for boxers of his size.As an amateur, Klitschko represented Ukraine at the 1996 Olympics, winning a gold medal in the super-heavyweight division. After turning professional later that year, he defeated Chris Byrd in 2000 to win the WBO heavyweight title. Klitschko's first reign as champion ended in an upset knockout loss to Corrie Sanders in 2003, which was followed by another upset knockout loss to Lamon Brewster in 2004. It was during this time that Klitschko hired Emanuel Steward as his trainer, which began an eight-year partnership that lasted until Steward's death in 2012. In particular, Steward was credited with Klitschko's transition from an aggressive puncher to a more defensively-oriented boxer, much as he had done with Lennox Lewis from 1995 to 2003.

From 2004 to 2015, Wladimir and his brother Vitali Klitschko (himself a multiple-time world champion) dominated heavyweight boxing, a period typically known as the "Klitschko Era" of the division. In 2006, Wladimir regained a portion of the world heavyweight championship after defeating Byrd in a rematch to win the IBF and IBO titles. He won his second WBO title by defeating Sultan Ibragimov in 2008. Following his defeat of Ruslan Chagaev in 2009, Klitschko was awarded the Ring title, and lastly he won the WBA title from David Haye in 2011. In September 2015, Klitschko was ranked as the world's best active boxer, pound for pound, by BoxRec; in November 2014, he reached a career peak of second best on The Ring's pound for pound list. After defeating Alexander Povetkin in October 2013 and until his loss to Tyson Fury in November 2015, Klitschko was recognized as the lineal champion by the Transnational Boxing Rankings Board.During Klitschko's reign as world heavyweight champion, his fights regularly generated a global television audience of 300–500 million viewers. Klitschko holds records for the longest cumulative heavyweight title reign of all time, with 4,382 days as world heavyweight champion, and most fighters beaten for the world heavyweight championship, at 23. He also holds records for the most wins and title defenses of the unified championship in professional boxing history. In 2011, both Wladimir and Vitali entered the Guinness World Records book as the pair of brothers with most world heavyweight title fight wins (30 at the time; 40 as of 2020). Klitschko was inducted into the International Boxing Hall of Fame Class of 2021, having been elected in his first year of eligibility.