Leonard's victory was unexpected
After Roy Jones Jr successfully unseated WBA heavyweight champion John Ruiz, BBC Sport looks back at other men who have risen through the divisions.
Jones Jr's audacious and successful bid to win Ruiz's heavyweight title on Saturday was one of the most significant challenges in boxing history.
The 34-year-old began his career as a junior middleweight and has been competing as a light heavyweight for the past five years.
He conceded 33lbs to Ruiz plus four inches in height.
But Jones Jr is not unique in rising through the divisions - other great boxers have sought challenges which define their careers.
Sugar Ray Leonard v Marvin Hagler, 7 April 1987
WBC middleweight title
With just one fight in five years, Leonard was attempting what many felt was an impossibility - he was challenging the most dominant champion in the world.
And he was doing that at middleweight, 13lbs heavier than his natural welterweight.
Leonard gambled on two things - that he still had the blinding speed to dazzle Hagler and that the champion was not quite the fighter of his prime.
The gamble paid off - Leonard had just enough skill to stay out of the ageing Hagler's way for most of the night and was rewarded with a split decision, which boxing fans still question to this day.
Success rating: 10/10 - Leonard's courage and nerve were flawless on the night.
Joe Frazier v Bob Foster, 18 November 1970
World heavyweight title
Foster was, like Jones, a terrific light heavyweight champion who could also punch very hard.
His large frame made him believe that he could easily compete with bigger men, but he would find very swiftly that he could not withstand heavyweight blows.
Frazier stopped him quickly in 1970, while in his prime, and Foster was also knocked out by Muhammad Ali during one of his other forays into the heavyweight division.
Success rating: 4/10 - Being tall is not the only key to being a heavyweight - you need a good chin as well.
Michael Spinks v Larry Holmes, 21 September 1985
IBF heavyweight title
Spinks had been the top light heavyweight in the world for over five years and had comfortably dealt with all challenges in front of him.
In moving up to heavyweight, he added bulk to his skinny frame and out-hustled Holmes for a controversial decision.
Holmes, who needed just one more win to equal Rocky Marciano's record of 49 consecutive victories, was irate at the judges' verdict and believed he was similarly unlucky in a rematch the following year.
Success rating: 7/10 - Spinks did well, had some luck and Holmes was ageing fast.
Pernell Whitaker v Julio Cesar Chavez, 10 September 1993
WBC welterweight title
Mexican Chavez was an unbeaten champion at three different weights, moving up from super featherweight to junior welterweight before challenging Whitaker.
Chavez was not effective at welterweight
The American was also a multi-weight champion, but had found it much easier to carry the extra poundage since moving up from lightweight.
The public had demanded to see the battle between two men considered to be the best in the world at any weight.
A combination of age, weight and too many wars seemed to catch up with Chavez when he took on Whitaker - despite gaining a draw, the majority opinion was that he was lucky not to have suffered his first loss.
Significantly, Chavez lost in his only other attempt at the welterweight crown.
Success rating: 5/10 - Chavez got a draw, but his performance deserved less on the night.