In Path of Radiance, Oliver is first seen at the Mainal Cathedral, applauding Empress Sanaki for her wit and charm, while claiming to be her most loyal supporter. This is later proven to be false as Oliver is working with Naesala to steal art from his fellow senators, and obtain laguz slaves including Prince Reyson of Serenes. Suspecting treachery, Empress Sanaki orders Ike to obtain evidence in order to prosecute Oliver. When Ike discovers Reyson, he leads an expedition into the Serenes Forest to either capture or kill Oliver. By joining forces with the Hawk tribe of Phoenicis, Ike is able to capture Oliver and gain the trust and support of Empress Sanaki.
Fire Emblem: Radiant Dawn
In Radiant Dawn, it is revealed that Oliver was being kept at his mansion in secret by his fellow senators, despite being stripped of his privilege by Sanaki and Prime Minister Sephiran. He initially fights against Ike and his comrades, but when he lays eyes on the Heron Prince Rafiel, he quickly switches to Ike's side, despite protests from the commander.