Role In God Of War II
In God of War II: Divine Retribution, Kratos encounters Atlas in his quest to find the Sisters of Fate. Atlas is at first reluctant to help Kratos given their previous encounter (See Below), yet Kratos is successful in convincing him that he no longer serves the Gods. Atlas therefore transfers to Kratos his powerful Atlas Quake move, and also bridges the gap, allowing Kratos to reach the Palace Of The Fates.
 Role In God Of War: Chains of Olympus
Queen of the Underworld, Persephone, planned to unchain Atlas from the world, thereby causing it's end and also the fall of Mount Olympus. In the final boss battle, Kratos re-chains Atlas to the world, foiling Persephone's plans. This would help to explain Atlas' reaction to Krato's in God Of War II.
Related ThreadsSome Quastions about Atlas.(Spoilers maybe) - last post by @ Aug 5, 2008
"Who Is Atlas" poster image - last post @ Oct 4, 2008