Champion boxer Muhammad Ali (formerly Cassius Clay) is a Muslim. He is a convert to Islam.
From: "Religious Affiliations of Celebrities" page in "Celebrity Religion" section of "Religion Facts" website (http://www.religionfacts.com/celebrities/religions_of_celebrities.htm; viewed 20 April 2007):
Below is an index of the religious affiliations or belief systems of celebrities (both living and dead; in film, television, music, literature, academics and politics), listed in alphabetical order by last name...
Celebrity: Muhammad Ali
Religion/Belief: Sunni Islam
Quotes, More Information, Sources:
The world-champion boxer converted to the Nation of Islam in 1964, and then to Sunni Islam in 1975. - Wikipedia [link to: http://en.wikipedia.org/wiki/Muhammad_Ali]