Eurus is a horse-like Immortal being who is the God of the East Wind. He sees the path of the Sun Chariot of Helios, and is one of the four horses that drives it, called the Fire Steeds.
Greek Mythology
Eurus was the Greek god of the East Wind. The four wind Gods are the sons of Eos Goddess of Dawn.
In God of War series
God of War: Chains of Olympus
Eurus was awakened by Kratos after Helios' disappearance, which led Morpheus to take control over the lands. After Kratos awakened him along with his brothers, the Horse Gods drove the Chariot of Helios right to where the Sun God himself was being kept; in the Underworld.
God of War III
While its is not currently stated, the Horse God of the East Wind is supposed to have driven the Chariot of Helios through the sky during the battle against Kratos and Perses. Later on, the Chariot of the God of Sun was crushed and Helios himself killed, and the Fire Steeds with him.