Epicurus is often regarded as the world's first atheist. Though he would hardly fit in with atheistic scholars today, he did have much to say about mankind's liberation from the fear that religion caused as he perceived it.
Epicurus maintained that the human body was composed entirely of atoms. Though he was technically correct in this regard, his understanding of atoms was far less informed than ours is today. Just as a human being thousands of years from today will think of our understand of atoms as primitive, we can see that Epicurus had a highly speculative understanding of atomic nature. He believed that atoms were different shapes and sizes, some shaped like hooks and others like eyes.
However, Epicurus did maintain that the universe was infinite and even expanding, and that is a position that many in the scientific community maintain to this day. In this regard, he was quite certain that whether or not there were gods was immaterial—for if they were there, they cared little for the affairs of humans. Epicurus felt that fear often brought out the worst in people, and that the fear of death in particular caused suffering among human beings. Epicurus maintained that one should not fear death or divine punishment. In a quote that is frequently attributed to him, he challenges the understanding of the nature of deities:
Is God willing to prevent evil, but not able? Then he is not omnipotent.
Is he able, but not willing? Then he is malevolent.
Is he both able and willing? Then whence cometh evil?
Is he neither able nor willing? Then why call him God?
This quote expresses the idea of an "all-loving, all-powerful god" as a logical fallacy. While it is certainly sweeping, it does assert his idea that to live in fear of gods or death is against the fundamental, curious nature of humanity.