Anthony Joshua and Joseph Parker will trade blows on March 31 for three world titles, with the winner eyeing a bout with Deontay Wilder to become undisputed heavyweight champion of the world.
Saturday's clash between IBF-WBA champion Joshua and WBO titleholder Parker is being billed as one of the division's biggest fights, but what were the best unification bouts in heavyweight boxing history?
From Joe Frazier's comprehensive win against Jimmy Ellis to AJ's back-and-forth battle with Wladimir Klitschko, ESPN takes a look back on previous world heavyweight title unification fights since the formation of the WBC in 1963.
Anthony Joshua vs. Wladimir Klitschko
April 29, 2017
IBF champion Joshua won the vacant WBA belt by knocking out Klitschko in the 11th round at Wembley Stadium, London. Joshua got up from a sixth round knockdown to floor former champion Klitschko three times in a thriller.
Klitschko announced his retirement after.
Wladimir Klitschko vs. David Haye
July 2, 2011
Haye lost his WBA belt to IBF-WBO champion Klitschko via a wide points decision at the Imtech-Arena in Hamburg, Germany. Afterwards, former world cruiserweight champion Haye blamed defeat on an injured little toe.
Wladimir Klitschko vs. Sultan Ibragimov
Feb. 23, 2008
Klitschko eased to a unanimous points win to earn a second world heavyweight title at Madison Square Garden, New York. It was the first unification bout in the division since Lennox Lewis outpointed Evander Holyfield in their 1999 rematch and earned IBF champion Klitschko Ibragimov's WBO belt.
Lennox Lewis vs. Evander Holyfield I & II
March 13, 1999; Nov. 13, 1999
Lewis got justice when he was crowned undisputed world heavyweight champion -- Britain's first since Bob Fitzsimmons' reign ended 100 years previously -- at the Thomas & Mack Center, Las Vegas. WBC king Lewis earned a unanimous decision over WBA-IBF champion Holyfield, who had held on to his titles via a controversial draw when the pair met at Madison Square Garden, New York, earlier in the year.
Evander Holyfield vs. Michael Moorer II
Nov. 8, 1997
Holyfield ended Moorer's resistance by a technical knockout in the eighth round, to add his WBA belt to his IBF title at the Thomas & Mack Center, Las Vegas. Holyfield knocked down Moorer five times to hold two of the three world titles. London-born Lennox Lewis held the WBC title.
Mike Tyson vs. Tony Tucker
Aug. 1, 1987
'Iron' Mike added Tucker's IBF belt to his WBA and WBC titles to become undisputed champion aged 21 at the Las Vegas Hilton. Tyson was the first undisputed world heavyweight champion -- holder of all the belts available -- since Spinks briefly ruled in 1978.
Mike Tyson vs. James Smith
March 7, 1987
Just a few months before becoming undisputed heavyweight champion, Tyson claimed his second world title with a win over the experienced James Smith. Tyson, just 20, widely out-pointed 'Bonecrusher' Smith, who was 13 years older, at the Las Vegas Hilton. It was not a thrilling fight as Tyson, making a first defence of the WBC belt, captured Smith's WBA title.
Joe Frazier vs. Jimmy Ellis
Feb. 16, 1970
Frazier floored Ellis twice in the fourth round and his fellow American failed to come out for the fifth round. Frazier captured Ellis' WBA belt and the vacant WBC title at Madison Square Garden, New York.