The term "Breton Kings" refers to the rulers of the historical region of Brittany in northwestern France. This area was known for its distinct culture and language, Breton, which is a Celtic language. The Breton Kings played a significant role in the region's autonomy and governance, especially during the medieval period when Brittany was often at odds with the French crown. The most notable of the Breton Kings was Duke Arthur I, who ruled in the late 12th century. The title of Duke was used instead of King, reflecting the feudal structure of the time. The Breton Dukes, including Duke John IV, sought to maintain their independence and often engaged in alliances and conflicts with neighboring powers, including England and France.