Once you get to act 6 you will unlock pantheon powers after you defeat act specific bosses. You can equip one major and one minor power to give yourself bonuses. You can also upgrade these powers to get more bonuses but that deals with a different achievement.
Major Gods
-Soul of Lunaris- killed at the end of act 8
-Soul of Arakaali- killed at the end of act 7
-Soul of Solaris- killed at the end of act 8
-Soul of the Brine King- killed at the end of act 6
Minor Gods
-Soul of Yugul- High Gardens act 8
Soul of Ralakesh- Ashen Fields act 7
-Soul of Shakari- The Sand Pits act 8 (subzone the oasis)
-Soul of Abberath- Prisoner's gate act 6
-Soul of Tukohama- The Karui Fortress act 6
-Soul of Ryslatha- The Wetlands act 6
-Soul of Grukhan- The Quarry act 9
Soul of Gruthkul- The Dread Thicket act 7