From David Remnick's King of the World:
When he became a Muslim, Ali would say that Clay was his slave name -- and that, of course, was true. But it was also a name in which his family took a certain pride. Cassius Clay was named for an abolitionist, a nineteenth-century Kentucky farmer who inherited forty slaves and a plantation called White Hall in the town of Foxtown in Madison County, Kentucky. Clay was six-foot-six and commanded troops in the war with Mexico. When he returned home, he became an abolitionist and edited an antislavery newspaper in in Lexington called The True American. He was one of the first men in the state to free the slaves on his plantation.
Clay ignored death threats and gave speeches in Kentucky denouncing slavery. "For those who have respect for the laws of God, I have this argument," he said, theatrically laying down a leather-bound copy of the Holy Bible. "For those who believe in the laws of man, I have this argument." Now he laid down a copy of the state constitution. "And for those who believe neither in the laws of God nor of man, I have this argument," and he laid down two pistols and a Bowie knife. During one debate with a proslavery candidate for state office, Clay was stabbed in the chest; luckily, he was carrying his Bowie knife and stabbed his assailant back. Abraham Lincoln sent Clay to Russia for the government, but he returned from St. Petersburg for more abolitionist activity. He maintained his physical courage till the end. When he was eighty-four, he married a fifteen-year-old girl.
