Why is Muhammad Ali called the greatest boxer of all time?

There were many great boxers, but many consider Muhammad Ali to be the greatest. This is likely due to the success that he had as a sportsman and as a social figure outside of the ring. Not only did he become the undisputed heavyweight boxing champion, and then regain the title later, he also resisted the draft for the Vietnam War (which stripped him of his boxing titles), he was a heavy racial pride advocate for African Americans during the Civil Rights Movement, he converted to Islam, changed his name to reflect the name, and enforced that others call him by his name, he won 2 Grammy awards for his music work, and became an accomplished author. Many successful boxers following Muhammad Ali also accredit him as an inspiration as well.