Robert Ingersall (1833-1899) was the preeminent orator of his generation, attracting millions of listeners across the nation. That he has been pretty much lost to history isn't all that surprising, given that history is largely written by people skittish of agnostics.
So, of course, are voters (then and now), and Ingersall quickly realized that his political ambitions were hopeless. But he remained a sought-after speaker, mesmerizing on all the issues of the day, not just his dissent to conventional religion. He constantly was attacked by both the orthodox Christian community and the far left for his Republican Party values. He answered well: "We are not endeavoring to chain the future, but to free the present. We are not forging fetters for our children, but we are breaking those our fathers made for us. We are the advocates of inquiry, of investigation, and thought."
He was instrumental in restoring the memory of the country's secular and rationalist heritage, rooted in the Enlightenment, to a generation of late 19th Century Americans. He said of the Founding Fathers:
"They knew that to put God in the Constitution was to put man out. They knew that the recognition of a Deity would be seized upon by fanatics and zealots as a pretext for destroying the liberty of thought. They knew the terrible history of the church too well to place in her keeping, or in the keeping of her God, the sacred rights of man. They intended that all should have the right to worship, or not to worship; that our laws should make no distinction on account of creed. They intended to found and frame a government for man, and for man alone. They wished to preserve the individuality of all; to prevent the few from governing the many, and the many from persecuting and destroying the few."
We have no figure comparable to Robert Ingersall in America today. We could use one.