Cassius Marcellus Clay

Cassius Marcellus Clay may refer to:
 * Cassius Marcellus Clay (politician) (1810–1903), American politician and abolitionist
 * Cassius Marcellus Clay Sr. (1912–1990), American painter and musician, named after the abolitionist, father of the boxer
 * Cassius Marcellus Clay Jr. or Muhammad Ali (1942–2016), American boxer