On this day, April 27, 1956: Heavyweight world champion Rocky Marciano retires and enters the history books

'The Brockton Blockbuster' was one of the greatest fighters who ever lived and 64 years ago to the day he decided to hang up his gloves

Rocky Marciano twice defeated Ezzard Charles during the final stages of his career, defending his world heavyweight title both times. AP Photo

When the never-ending debate about the greatest boxers in history gets discussed, Rocky Marciano is rarely near the top of the list.

Not that he is  totally ignored, he just is not talked about in the same regard as the likes of Muhammad Ali, Sugar Ray Leonard, Joe Louis, or Sugar Ray Robinson.

Even if the debate was narrowed down just to the greatest heavyweights, Marciano would, instinctively, be mentioned by many after Ali, Louis, Jack Dempsey, Jack Johnson, and possibly even Mike Tyson by the younger generation.

Yet, Marciano, whose knockout punch packed "more explosive energy than an armour-piercing bullet" according to a study, deservedly earned his place in the annals of boxing history.

The only heavyweight world champion to end his career undefeated, Marciano decided, after 49 fights and 49 wins (with 43 knockouts), to retire at the age of 32 on this day - April 27, 1956.

The first 16 of those professional fights ended in knockout wins for Marciano, all before the end of the fifth round and nine inside the opening round.

It was not until his 26th fight did the Brockton, Massachusetts native get truly challenged when, in March 1950, he earned a split decision win over Roland La Starza. It was the closest any fighter would get to beating Marciano.

Marciano's first major high-profile fight came in October 1951 when he fought the great Joe Louis and stopped the former world champion in the eighth round in what would be Louis' final fight.

Four more wins would follow before Marciano earned his first world title shot, where he would face Jersey Joe Walcott in September 1952. Walcott dropped Marciano in the first round and began to build a points lead, only for the challenger to produce a devastating right hook in the 13th round to claim the title.

An immediate rematch was granted but this time the outcome was far more emphatic, Marciano delivering a first-round KO to send Walcott into retirement.

Marciano defended the world title five more times, defeating La Starza again - this time by 11th-round KO - twice beating Ezzard Charles - first on points then by eighth-round stoppage - taking out Don Cockell in the ninth round, and completing his career with another ninth round stoppage of Archie Moore.

Around six months later, Marciano decided to call it quits and walked away from boxing as the undisputed heavyweight champion of the world.

Just over 13 years later, on August 31, 1969 - the day before his 46th birthday - Marciano was killed in a plane crash.

A member of the International Boxing Hall of Fame, Marciano holds a number of records and accolades that have earned him his place among the sport's greatest.

He was named The Ring fighter of the year three times, holds the highest knockout percentage (87.76%) of any heavyweight champion in history over the course of a completed career, and his 1952 KO of Walcott has been named in a poll as the greatest knockout in boxing history.