Guillaume Cale (sometimes anglicized to William Kale, also known as Guillaume Caillet, popularly known as Jacques Bonhomme ("Jack Goodfellow") or Callet) was a wealthy peasant from the village of Mello near Beauvais, who became leader of the peasant Jacquerie which broke out in May 1358 and continued for a month unchecked until the Battle of Mello on 10 June.
It was still prosperous despite the impact of the Black Death, and maintained its wealth under the protection of the household troops of the French king and the other nobles who lived in and around Paris, depending on the region for food and for taxation income.
Cale was sympathetic to the Parisians, and so when a similar rebellion began to ferment in the Beauvais region, he rose to become its leader, forming bands of peasants, villagers and brigands into a fairly cohesive though ill-equipped force.
Loosely organized, the rebel bands ran amok, killing hundreds of nobles, retainers, and their wives and families amid scenes of brutality.
Cale was joined by contingents from the towns of Senlis, Clermont and Creil and eventually could field 5,000 men, including several minor nobles, whose military experience gave his force structure.