Well... kind of an atheist. He does not believe in a supreme being.
Rep. Fortney "Pete" Stark, D-Calif., is the first openly "nontheistic" member of congress, the Secular Coalition for America announced Monday, March 12.
Of course, he's a Unitarian. I attended a Unitarian service a few years back as part of a survey of religion course. It was weird and made me feel uncomfortable.