(CNN) -- There are not many sportsmen who can call themselves "The Greatest" and not be greeted with ridicule -- former world heavyweight champion Muhammad Ali is one of the few who can lay claim to such unrivaled supremacy.
The Kentucky native turned 70 Tuesday, prompting people from across the world to pay tribute to a former boxer who has shown his fighting spirit both inside and outside the ring during an extraordinary life.
"Everything that Ali has done and stood for, you can only aspire to be like him," Tris Dixon, editor of Boxing News, told CNN. "He was the king in the biggest and best era of heavyweight champions."
Ali rose to prominence at the 1960 Olympics in Rome, where he won a gold medal in the light heavyweight division fighting under his birth name of Cassius Clay.
After converting to Islam in 1964, Clay was renamed Muhammad Ali and went on to participate in some of the most memorable contests in the history of sport.
Ali's boxing career is perhaps best remembered for two of his most famous fights against two of his fiercest rivals.
In Zaire in October 1974, Ali upset the odds to reclaim the WBA and WBC world heavyweight titles against George Foreman in a bout dubbed the "Rumble in the Jungle."
A year later, Ali squared off against the late Joe Frazier for the third time in his career.
The fight in the Philippines, known as the "Thrilla in Manilla," lasted 14 devastating rounds, with Ali taking glory when Frazier was unable to make the bell at the start of the 15th.
But, for Dixon, it was a third-round knockout of Cleveland Williams in a 1966 fight for the world heavyweight title which best displayed Ali's boxing talents.
"Against Cleveland Williams, that was Ali at his best," he explained. "It was utter poetry. It was just immense ... it was punch perfect against a world-class opponent."
Ali eventually retired in 1981 with a record of 56 wins, 37 by knockout, and five losses in 61 bouts.
He began an altogether different fight in 1984, when he was diagnosed with neurological disorder Parkinson's syndrome.
In 1996, at the age of 54, Ali provided one of the iconic images of the Atlanta Olympics when he lit the torch to declare the Games open.
Ali also received a replacement gold medal for the one he had won 36 years earlier, having thrown the original into the Ohio River after being refused entry to a restaurant.
Despite Ali's advancing years, Dixon claimed his legacy is still as strong and relevant as it has ever been.
"There will never be anyone like Ali," he said. "There will be people like Tiger Woods and Michael Jordan who reflect their times, but there will never be someone who means as much to the world and the cultural landscape as much as Ali did."