Clay was the son of Greene and Sally Clay. Born 1810 and died 1903. Known as the " Lion of Whitehall", Clay was a cousin of Henry Clay; abolitionist; Ambassador to Russia; and Union General.
Cassius Clay was a pioneer, a southern aristocrat who became a prominent anti-slavery crusader. He was a son of Green Clay, one of the wealthiest landowners and slaveholders in Kentucky. Clay worked toward emancipation, both as a Kentucky state representative and as an early member of the Republican Party. He spent 25 years of his life publishing "The True American" before Lincoln tapped him and asked, "Tell me about your Proclamation of Emancipation."
Clay attended Transylvania University and then graduated from Yale College in 1832. While at Yale, he heard abolitionist William Lloyd Garrison speak, and Garrison's lecture inspired Clay to join the antislavery movement. Garrison’s arguments were to him “as water is to a thirsty wayfarer.” Clay was politically pragmatic, supporting gradual legal change rather than the immediacy of the Garrisonians. 
Clay served three terms in the Kentucky House of Representatives, but he lost support among Kentucky voters as his platform became more focused on ending slavery. His anti-slavery activism won him enemies. During a political debate in 1843, he survived an assassination attempt by a hired gun, named Sam Brown, and despite being shot in the chest, and being restrained by the attacker's confederates, he defended himself, seriously wounding his attacker with his Bowie knife and throwing him over an embankment.
In 1845, he began publishing an anti-slavery newspaper called the True American in Lexington, Kentucky. Within a month he received death threats, had to arm himself, and had to barricade the doors of his newspaper office for protection. Shortly after, a mob of about sixty men broke into his office and seized his printing equipment, which they shipped to Cincinnati, Ohio. Clay continued publication there.
Again in 1849 while making a speech for slave emancipation he was attacked by the six Turner brothers, who beat, stabbed and attempted to shoot him, in the ensuing fight Clay fought off all six and killed Cyrus Turner after regaining his Bowie knife that had been taken from him earlier in the fight.
Even though he opposed the annexation of Texas, Clay served in the Mexican-American War as a Captain from 1846 to 1848. His connections to the northern antislavery movement remained strong, and he was a founder of the Republican party and a friend ofAbraham Lincoln, supporting him for the presidency. Clay was briefly a candidate for the vice presidency at the 1860 Republican National Convention, but lost the nomination to Hannibal Hamlin.