David Eddings Wiki
This page is written in the in-universe perspective of the "Garion" series' of novels.

Oldoran was the Duke of Asturia when the sorceress Polgara first came to Arendia. A hopeless alcoholic, he was openly mocked by his court, particularly the Baroness Asrana and Earl Mangaran. Far worse, when Polgara arrived, he'd fallen under the influence of a Dagashi who was posing as an agent of Tolnedra, and who had promised the Empire's aid in Oldoran's plot to make war against the rival duchies of Mimbre and Wacune. Needless to say, the promised aid would never have materialized, and if Oldoran had acted, it would have likely resulted in the other two duchies teaming up and eliminating Asturia.

Having decided that Oldoran was too far gone to be convinced of the error of his ways, Polgara plotted with Asrana and Mangaran to have Oldoran removed in favor of Mangaran. She staged an assassination attempt on Oldoran's life, then used her mental abilities to make him temporarily insane so that he would be declared unfit to rule. Afterwards, he spent the rest of his life locked up while Mangaran took over. Oldoran himself died only a few months afterwards from extensive liver damage caused by years of drinking.

Unfortunately, Mangaran died a few years later of natural causes, and his heir, Olburton, was unable to hold on to power, resulting in Oldoran's nephew Nerasin becoming the new Duke of Asturia.