Ann Rand
A well known atheist, individualist and radical libertarian/anarcho-capitalist author who you'll probably be forced to read in High School or College. Her magnum opus was the 1000-page "Atlas Shrugged", one of the longest novels ever written in English.
"Let no man posture as an advocate of peace if he proposes or supports any social system that initiates the use of force against individual men, in any form." Ann Rand