Bart Ehrman is a New Testament scholar in the field of textual criticism of the New Testament. An atheist, Ehrman is a professor of Religious Studies at the University of North Carolina.
Some people doubt that Jesus actually existed. They claim that some first-century men made up a story, and that a bunch of people were fooled into believing it. I've heard from a lot of skeptics of Christianity, and there's a fair number who claim that Jesus never actually existed.