An atheist is a person who does not believe in any god. In contrast, theists believe in a god and agnostics say that whether a deity exists is unknown or unknowable. Although atheism itself is centuries old, the development of so-called "new atheism" has made atheist a popular tag.
The new atheism movement is attributed in part to a variety of 21st-century books more outspoken and critical of religion than earlier atheist works. The authors included Richard Dawkins, Sam Harris and Christopher Hitchens.