This, according to a thirteenth-century fable, was a poor woodcutter who transported his wood on an ass, whom Merlin assisted by showing him treasure, on condition of his being kind to the poor. Each year he had to return to tell the wizard how he was getting on.
As the respect with which he greeted Merlin diminished each year, his fortune was eventually taken from him.
See also
Wizards and Enchanters | The Crypt