|“||The Caves of Mount Olympus hold the flame that spawned all others: the Primordial Fire which long ago was stolen and given to man by the Titan Prometheus. It is the source of Helios' energy.||”|
The Primordial Fire is the fire that was stolen by the Titan Prometheus and given to man, an act he was severely punished for. The fires are also known as the Fires of Olympus.
In God of War: Chains of Olympus
In God of War: Chains of Olympus, while in the Caves of Olympus, Kratos is tasked by Eos to find the Primordial Fire found deeper within the caves. It is the flame that gives the God Helios his power. When Kratos obtains it, he must then use it with the Sun Shield to destroy three statues that shoot fireballs via gigantic shields.
When Kratos acquires the fire, it powers his Sun Shield and grants him the ability to reflect projectiles back at enemies.