Guillaume Le Boucher, Boucherii, Carmelite, was made a licentiate in theology at the University of Paris in December, 1413; he is referred to as doctor at the time of the Trial. He was then living in his house at Rouen, and had lived there since 1422.

Guillaume Le Boucher was very diligent at the Trial and he judged Jeanne to be an apostate and guilty of heresy. He pretended to depend on the authority of Gilles de Duremort, Abbot of Fécamp.