Muhammad Ali is the son of Cassius Clay Sr. and Odessa Lee Grady Clay.

One of Odessa Clay's grandfathers, Abe Grady, was an immigrant from County Clare Ireland. Abe Grady married a black woman when he came to the U.S.

The source of this information is David Remnick's King of the World.

Other information on intermarriage between African and Irish Americans during the 19th century can be found in:

The History of Black Catholics by Cyprian Davis; relates the story of the notable Healy family that produced many Catholic religious.

A History of the Irish in New York City Chapter 4 "Desirable Companions and Lovers"; Irish and African Americans in the Sixth Ward, 1830-1870 by Graham Hodges; the intermarriage between Blacks and Irish in the notorious Five Points district is treated.