Jean de Meung's abilities were more poetic than alchemical and his Roman de la Rose was far more memorable than his treatise on the hermetic philosophy. He was born around the year 1280, and he was so known for his love of humour and wit that it's not certain how sincere his praise of alchemy actually was. It was common for poets of the medieval period to oppose the priesthood, and he composed a powerful posthumous satire about their greed.
He left a heavy chest to the Cordeliers in his will, and as he was renowned for his interest in alchemy they accepted it, believing that it held the results of his search for the Philosopher's Stone. In fact, he had filled the chest with large pieces of slate etched with unintelligible symbols. It seems unlikely that the player of such a practical joke was genuinely a believer in alchemy.