Perhaps more due to Ad Avis' powers of mind control rather than a lapse of judgement on his part -- although the world may never truly know -- Arus allowed Ad Avis to become his vizier. Some time afterwards, he vanished. Unbeknownst to all save the vizier and the emir, he had been transformed into a Riding Saurus who would sometimes be known as Roget the Saurus. Somehow, the transformed emir ended up in the possession of Ali Fakir, the traveling used saurus salesman.
While in Shapeir, Ali Fakir sold the hapless saurus to the Hero. The emir immediately recognized the Hero's bravery and hoped that this would be the key to his restoration. He provided the Hero with transportation across the Shapeirian Desert for a few weeks, before growing restless. Eventually, he followed the Hero to Aziza Home, where Aziza discovered the enchantment he was under. She kept the saurus with her until the Hero could stop whatever evil was afoot.
After the defeat of Ad Avis, a dispel potion was administered at the adventurer's Hero Ceremony. There, finally himself again, Arus al-Din spoke on behalf of the Hero. Soon, he retired as the emir of Raseir, passing on the title to his neice Zayishah.