Cleaning up the world heavyweight titles and holding all four belts eluded the likes of Lennox Lewis, Evander Holyfield, Mike Tyson, Riddick Bowe and Wladimir Klitschko.
But in 2018, boxing could have its first WBC-WBA-IBF-WBO world heavyweight champion if -- and it's a big "if" -- the fights get made and the world governing bodies do not insist on mandatory defenses to scupper unification fights.
It could be just two fights away.
Following the announcement of Joshua-Parker for the WBA, IBF and WBO world titles on March 31 at Principality Stadium in Cardiff, Wales, confirmation came last Friday that WBC champion Deontay Wilder is to face Luis Ortiz at Barclays Center in Brooklyn, New York, on March 3.
Joshua and Wilder are favorites to win their fights, but it is not as simple as them both progressing from semifinals to meet each other in a final for four world title belts by the end of 2018.
Here, ESPN looks at what the announcement of Joshua-Parker means for the heavyweight division.
Joshua-Parker is significant as it will unify three versions of the world heavyweight title for the first time since Wladimir Klitschko beat David Haye for the same belts in July 2011.
Klitschko kept those belts intact by walking a tightrope of fulfilling various mandatory defenses by certain deadlines until he lost them in an upset points decision to England's Tyson Fury in November 2015.
Fury was then stripped of the IBF belt shortly after his triumph for agreeing to face Klitschko in a rematch, rather than the IBF mandatory challenger Vyacheslav Glazkov. The belts became fractured again when Fury declared he was mentally unfit to face Klitschko again.
Joshua went on to quickly deal with American Charles Martin, who had beaten Glazkov, for the IBF belt in April 2016, then claimed the vacant WBA title after knocking out Klitschko in 11 rounds last April.
Joshua, who lives in north London, now wants New Zealander Parker's WBO strap before moving on to American Wilder.
Joshua, 28, stated before and after his last fight -- a 10th-round stoppage win over Carlos Takam on Oct. 28 -- that his aim for 2018 is to hold all four world heavyweight titles.
But only two male boxers have unified all world titles since the WBO became the fourth belt available in 1988.
American Terence Crawford, ESPN's 2017 fighter of the year, unified all four junior welterweight world titles when he knocked out Namibia's Julius Indongo in the third round in August last year. The Nebraska native then gave up the belts to pursue new goals in the welterweight division.
The other male boxer of the four-belt era to unify the major sanctioning organization titles was Bernard Hopkins in 2004. Hopkins stopped fellow American Oscar De La Hoya to win the only world middleweight belt not in his possession and made one defense of all four belts before losing them to Jermain Taylor, who was stripped of a belt by the time they met in a rematch.
Klitschko, who retired last year, never had the opportunity to fight for the fourth world title as IBF-WBA-WBO champion because his elder brother Vitali was WBC champion at the time. The Ukrainians kept a promise to their mother that they would never fight each other.
Anything other than a Joshua KO will be a surprise.
The Briton is a huge 1-25 favorite with U.K. bookmakers, and his wins over the likes of Klitschko, Takam, Dillian Whyte and Dominic Breazeale, along with his Olympic triumph, suggest Joshua will have too much for Parker.
Joshua (20-0, 20 KOs) has achieved more and has a better knockout record and selection of punches. He also dealt with Takam better after the France-based boxer took Parker to points in 2016. Joshua has faced tougher tests than Parker -- Klitschko, but arguably his British rival Whyte, too.
While Joshua has shone as champion, Parker (24-0, 18 KOs) failed to impress after a majority points win over England's Hughie Fury at Manchester Arena on Sep. 23.
But the New Zealander, who turned 26 on Jan. 9, has shown he is capable of beating bigger men like Alexander Dimitrenko and Kali Meehan, both former world title challengers whom he stopped in three rounds.
Not really. Joshua is a huge star in the U.K. -- much bigger than Wilder is in the U.S. -- and also perhaps the best-known boxer in the world with Floyd Mayweather retired again.
Joshua has attracted crowds of 90,000 and 78,000 to his past two fights, with growing global television audiences.
It is not just the entertainment he brings to the ring -- 20 straight knockouts as a professional since winning an Olympic gold medal as an amateur -- his lack of trash talking and humble personality have endeared him to audiences beyond hardcore boxing fans.
Joshua's spectacular win over Klitschko last year elevated his profile to a new level. In June, he was named the world's most marketable athlete by the sports industry magazine SportsPro, ahead of basketball's Stephen Curry, soccer's Paul Pogba, MMA's Conor McGregor and cricketer Virat Kohli.
Joshua has an impressive list of commercial partners -- unusual for a boxer -- such as Under Armour, Beats By Dre, Lucozade Sport, Lynx, Jaguar Landrover, Audemars Piguet and Dubai Tourism.
But all of that -- Joshua's reputation in the ring, appeal to fans and marketability -- would be damaged by an upset loss to Parker.
Defeat would also scupper plans for big fights against the likes of Wilder, Tyson Fury and perhaps David Haye, which in turn would affect the global interest in boxing.
The first job as unified champion will be to keep the WBA happy, before exploring the possibility of a fight against the winner of Wilder-Ortiz.
The WBA's new mandatory contender is Alexander Povetkin (32-1, 23 KOs), who outpointed Romania's Germany-based Christian Hammer in a title eliminator last month.
Before another unification fight with the WBC champion, the Joshua-Parker winner may have to fight Povetkin first. That would most likely push back Joshua-Wilder, or Parker-Wilder, until 2019.
Povetkin -- unanimously outpointed by Klitschko in 2013 -- will also be an unpopular fight for Joshua or Parker because the Russian has had multiple doping offenses.
Povetkin, 38, twice failed random Voluntary Anti-Doping Association drug tests in an eight-month span in 2016. The first cost him a shot at Wilder's WBC belt.
Povetkin is also in a good position with the WBO since Hammer was No. 1 in its rankings (Povetkin was No. 6).
Keeping three versions of the world title intact is difficult to maintain. Fury and Lewis found it impossible, although Klitschko managed it from 2011 to 2015 during the second-longest heavyweight title tenure in history (nine years and seven months).
London-born Lewis also unified three versions of the world heavyweight title with a points win over Holyfield in November 1991. Lewis, the WBC champion, claimed Holyfield's WBA and IBF belts with a points win. The WBO heavyweight title, then held by Vitali Klitschko, was still in its infancy and not universally recognized as it later was. Lewis was also stripped of the WBA belt after beating Holyfield.
The winner of Joshua-Parker will at least have time from the IBF since Joshua's win over Takam was a mandatory defense.
Good, but both may have to win two fights to set it up -- and so push back a fight for four world heavyweight titles to 2019.
Just as Joshua is the overwhelming favorite to win on March 31, Wilder is expected to prevail over Cuba's Florida-based "King Kong" Ortiz (28-0, 24 KOs), who is 38 and ranked No. 3 by the WBC.
Wilder (39-0, 38 KOs), 32, from Alabama, will make a sixth title defense against Ortiz, who tested positive for two banned diuretics in a random drug test, causing a fight with Wilder to be postponed in November. Wilder instead knocked out mandatory challenger Bermane Stiverne in the first round on Nov. 4.
Wilder may also have to get past his No. 1 challenger -- currently Jamaica-born Londoner Whyte -- before a four-title showdown.
Provided Wilder and Joshua keep on winning, the next battleground will be the negotiating table. But Joshua's deal with Parker, who has secured 30 to 35 percent of the purse, offers hope. Wilder will want a bigger cut than Parker, but Joshua will want more than a 50-50 split.
Joshua's ambition of three fights in 2018, climaxing with Wilder, is ambitious. A 2019 meeting, either at London's Wembley Stadium in the spring or the T-Mobile Arena in Las Vegas, is perhaps more likely.
Joshua's English rival Fury (25-0, 18 KOs) still considers himself the lineal world heavyweight champion, but he has not fought since November 2015.
The 29-year-old from Lancashire is likely to get his boxing license back this month after a doping violation was backdated.
Fury, who has cited problems with depression and cocaine use, regularly calls for Joshua and Wilder to fight him on social media.
But Fury needs to put together a series of wins and go from being court jester to contender if he is to fight the heavyweight king again.
If Joshua and Wilder collide in the next 18 months, Fury will have to be content to get in line and hope to be first in the queue to meet the new undisputed champion.
Joshua's promoter, Eddie Hearn, is not contemplating a fight with Fury anytime soon.
"This fight is unmakeable," Hearn recently said. "It's not even as if we are within 5, 10, 15 or 20 percent. Fury is a voluntary challenger for two titles.
"Let's make it clear that he has a lot of value in the fight. It's not like we see him as 20 percent. But at the moment, we should not even be considering this fight until we see if he can actually do something rather than just talk about it."