Author Susan Jacoby tells a story of a man who gave up politics to preach religion in her new novel The Great Agnostic: Robert Ingersoll and American Freethought.

According to Susan Jacoby, Robert Ingersoll is a forgotten hero of the 19^th century who was, according to the author "one of the most famous people in America in the last quarter of the 19th century."

"He went around the country," Jacoby tells NPR's Rachel Martin. "He spoke to more people than presidents. He was also an active mover and shaker behind the scenes of the Republican Party."

So why doesn't people know of this forgotten hero? Jacoby reveals through her book, that his only crime was to support Darwin's theory and fight publicly against government interference in religion.

"Because of this, as The New York Times said in his obituary when he died in 1899, he couldn't run for public office even though he was a big deal behind the scenes," she says. "Because even then, although most of the Republican presidents from Lincoln on didn't even belong to a church, you still, if you were an open agnostic or atheist, could not hope to run for public office."

Jacoby also reveals that Ingersoll actually gave up his political career to preach the wrong doings of a fundamental religion.

"He had enormous audiences," Jacoby says. "The late 19th century, we think of this as the Victorian era, and stuffy and all that, but it was a time of enormous change" as Americans began to discover Darwin, and immigration changed the social makeup of the country. "Ingersoll was probably the first person who said, 'I don't believe in a God,' that a lot of people had ever seen."

Ingersoll had no fear of asking controversial questions publically. He was not scared to offending neither the government nor the church. Ingersoll's father himself was a Presbyterian minister.

"He wanted to revive the secular portion of America's revolutionary history," Jacoby continues. "He did not want to deny the role of religion in the founding of America, but he wanted to put it in its perspective." Then as now, she adds, many people asked whether America had been founded as a Christian nation. "As controversial then as it is now, Ingersoll's answer was no, and he went around explaining why it was no."