11. Rocky Marciano
We all know about the legend that is Rocky Marciano. Due to his in-ring prowess, he is the only undisputed heavyweight champion to have retired from the sport with an unbeaten record. In short, he defended his title six times. Marciano went 49-0 in an incredible career thanks to his heavy hands, durability, stamina, and relentless nature.
The Brockton Blockbuster actually started boxing when he was drafted into the Army in 1943. He reportedly only started the sport to get out of kitchen duty. The army served him an honorable discharge in 1946, following the end of the war. That’s when he made the decision to pursue a professional career. And the rest is history.