Oreius was a loyal servant of Aslan, going to his side even before the promised human monarchs arrived. Likely he was one of the Narnians who recruited his countrymen for service in Aslan's army. He, Aslan, and the rest of the Narnians gathered together at Aslan's Camp in 1000 NY, where he was made Aslan's general. He was present at the first arrival of Peter, Susan, and Lucy at Aslan's Camp. Shortly after their arrival, he rushed to the aid of the future queens when they were attacked by two wolves. The sisters were, however saved by their brother, and Oreius and his soldiers were commanded to follow the fleeing wolf Vardan to the White Witch's camp. They did so, quickly storming the encampment and rescuing Edmund. They quickly returned him to safety at Aslan's Camp.
The next day, Oreius was wakened early to be told that Aslan had gone away in the night and been killed by the Witch at the Stone Table. He was present when Peter confirmed Aslan's disappearance. Despite the death of his king, he affirmed his loyalty by asking the prince for orders. Later that day, the entire Narnian army marched to the Battle of Beruna, with Oreius and Peter leading them. Oreius fought beside the prince during the initial attack. When the army retreated, Oreius was ahead of the prince as the army rushed into the gorge they had chosen as their secondary battlefront. When Oreius was made aware that the prince had been thrown off from his unicorn and wounded, and faced serious threat from Queen Jadis herself, he rushed back along with a rhinocerous to save him. As he fought to reach his ruler's side, General Otmin of the White Witch's Army attempted to stop him, and was killed. When Oreius reached the Queen, he attempted to kill her, and was turned to stone.
Shortly afterwards, Oreius was revived by Aslan. He was present at the coronation of the Kings and Queens, and presumably served them afterwards as well. At some point, he married and had descendants.
Oreius was played by Patrick Kake in the Disney and Walden media film of The Lion, the Witch, and the Wardrobe.
Oreius is not in the books.
Oreius is the direct ancestor of Glenstorm, another Centaur general who served under Caspian X.