Rocky Marciano is best known for being the only world heavyweight champion to retire with an unbeaten record. However, he is also admired for the determination with which he transformed his natural gifts, which were by no means the best in the business, to such effect.

When Marciano was first presented to Charley Goldman, his long-time trainer, Goldman's assessment was: “If you done anything right, I didn't see it.” Born Rocco Francis Marchegiano in 1923 (his manager later persuaded him to lose the middle “heg”), he nearly died of pneumonia before he was 2 but was put on the road to recovery by a great aunt who used an old Italian remedy of trickling warm water into his mouth from a spoon.

His initial sporting ambition was not for boxing but for baseball. He was given a try-out by the Fayetteville Cubs, a minor league team, but lasted only three weeks before returning to Brockton, his home town, to dig ditches for a living before the boxing started in earnest.

Marciano's first professional bout, on March 17, 1947, resulted in a third-round knockout of Lee Epperson. His career is interesting thereafter because the baseball flirtation followed, and it was after this that he returned to the amateur boxing ranks.

We can therefore ask if Marciano really had a 49-bout unbeaten run because, back in the amateurs, he recorded a succession of wins but lost in the All-Eastern Golden Gloves Championship to Colley Wallace, a highly rated amateur. So while he was unbeaten as a professional, Marciano's winning streak faltered at the start.

Marciano became world champion when he defeated Jersey Joe Walcott in Philadelphia in September 1952. He staged six defences of his title, including a brutal clash with Ezzard Charles, when his face was cut so badly that the referee was about to stop the bout before Marciano floored his opponent in the eighth round.

Marciano retired after defeating Archie Moore in 1955. Despite lucrative offers, he resisted making a comeback. In 1969, he died as one of three passengers in a plane crash.

The invincibles

Rocky Marciano (1947 to 1955, 49 wins, 43 knockouts, no draws) Remains the only unbeaten world heavyweight champion, but lost an amateur fight after turning professional.

Joe Calzaghe (1993 to present day, 45 wins, no draws, 32 knockouts) Boxes Roy Jones Jr tonight and has suggested that he will retire thereafter. Few are convinced that he will resist the financial temptations of a return.

Sven Ottke (1997 to 2004, 34 wins, no draws, six knockouts) German super-middleweight. That he has not fought Calzaghe is a stain on both men’s careers.

Floyd Mayweather Jr (1996 to 2007, 39 wins, no draws, 25 knockouts) “Pretty Boy”, a true ring artist, retired unbeaten after cutting Ricky Hatton to pieces last December.