He was the advisor to László's father János VI before he was advisor to László, and his age and experience made him extremely useful. He would apprise László of events that were currently causing problems for the kingdom, and remind him of tactics which had been used successfully by his predecessors.
He also saw it as his duty to remind László that, at thirty-three, László really ought to be married and producing heirs to the throne (László did not thank him for these reminders). Eventually, Rezső managed to convince László that the daughter of the Count of Mordfal, Mariska, would make a potentially suitable consort, and László agreed that Rezső could invite her to the Palace.
While Rezső took no part in the final conflict, he too was crushed by falling stone blocks when the Tree renewed the Palace.