Excerpts taken from the Oxford Classical Dictionary:

The Titan son of Iapetus and brother of Prometheus. In the Odyssey, he… holds the tall pillars which hold earth and heaven apart, and in Hesiod he lives at the edge of the world and holds up the heaven. From an early date, associated with Heraclean legends. Heracles askes Atlas to get the golden apples for his eleventh labor while he held up the sky.

Excerpts taken from the Encyclopedia of Mythology, Eric Flaum:

Atlas and his family ruled over Atlantis, an enormus continent out beyond the Pillars of Heracles. The family was perceived as becoming too greedy , which caused Zeus to allow the destruction of Atlantis. Atlas escapes and becomes allied with Cronus and the Titans against Zeus and the Olympians. Zeus is victorious, and as the leader of the unsuccessful revolt, Atlas was subjected to the most serious punishment: he was made to support the celestial globe upon his shoulders for all eternity.