In my case, it was a magazine article I read about the Turin Shroud and its possible manufacture by Leonardo da Vinci. Once I got my hands on the internet I googled for it and discovered the excellent Jesus Never Existed resource. From there it was but a step into the site's own forum and then I never looked back.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'