Muhammad Ali could have attained a perfect winning record before retiring in 1981 if not for the five challengers that got in the way of his boxing career.
In 1971, Muhammad Ali was on his 32nd winning streak when he fought and lost to Joe Frasier in New York City via a unanimous decision.
Since then, Muhammad Ali lost to five more equally great boxers before finally retiring.
After retiring from boxing, Ali was diagnosed in 1983 and found to be suffering from Parkinson's disease. Despite his disability he remains a public figure and was instrumental in setting up a foundation that helps people suffering from Parkinson's disease.
Here are five of the great boxers that prevented Muhammad Ali from attaining an unblemished record in his professional career.