Question: what do you call a person who doesn't believe in god?
Answer: A person who rejects belief in gods is called an atheist. Theism is the belief in one or more gods. Adding an a, meaning "without", before the word theism results in atheism, or literally, "without theism". Atheism is not the same as agnosticism: agnostics say that there is no way to know whether gods exist or not.