For Stiefel, a slim, scruffy ex-Catholic, his public persona is his wallet and activism. Through the Stiefel Freethought Foundation, the 38-year-old has made an indelible impact on the nation’s fastest-growing “religious” group: the nonbelievers. Most of the highest-profile atheists campaigns –- flashy billboards in high-traffic areas, news-making efforts to get atheists to come out of the closet, and boisterous rallies - are funded by his fortune.

Stiefel isn’t shy about his far-reaching goals.

“What I am trying to accomplish is multifold, he told CNN. “I consider myself working on the next civil equality movement, just like women’s rights, LGBT rights and African-American Civil Rights. We are still in the early stages of eliminating discrimination against atheists and humanists. That is something I really want to accomplish.”

So far, Stiefel has pumped $3.5 million into those aspirations, and his money benefits a number of atheist organizations, from the Clergy Project, a group that helps atheist and doubting clergy out of the closet, to American Atheists, arguably the most in-your-face atheist group in the country.

Stiefel sees his work as far more than just money. For him, this is just the beginning.

From Catholic school to atheist millionaire

Stiefel was born in Albany, New York, in 1974 to Catholic parents. He was raised in a Catholic household, confirmed in the church,d attended Sunday school, went to a Catholic high school.

“I was a cross-wearing, praying, religious-retreat Catholic,” Stiefel said. “You could say there were points that I felt the spirit.”

But his faith, he said, fluctuated during high school. “I was always a skeptic,” he said, “and I always asked a lot of questions.”

At 18, Stiefel attended Duke University to pursue a degree in psychology. To fill an elective, he took an Old Testament history class at the Duke University Divinity School. It was there, he said, that his final “ebb” away from belief took hold.