Burning Tower by Larry Niven
Whandall Placehold was two years old when a lordkin - possessed by the firegod - burnt his city to the ground. Five years later the god entered another of the lordkin - and once again the city burned. But when the firegod attempted to master Whandall it discovered he was unlike the other lordkin, for Whandall resisted the urge to burn his city and sought instead to bend the firegod to his own will. Now Whandall continues his quest to find the dark truth of the firegod's power - and to free the lands he has usurped.