William I, Duke of Bavaria

William Wittelsbach (1330–1389), second son of Emperor Louis IV and Margaret of Hainaut, was Duke of Bavaria-Straubing and Count of Holland, Hainaut and Zeeland. His rule began as a war with his own mother: when the nobles of Holland called Margaret back in 1350, the Cod and Hook leagues formed and civil war followed.

Edward III came to her aid, yet William won at Zwartewaal in 1351 after losing the naval battle of Veere. In 1354 she recognised him as Count of Holland and Zeeland, and her death in 1356 left him Hainaut as well.

He lost his reason after returning from England in 1357 and killed his knight Gerard van Wateringe. His brother Albert became regent in 1358, and William spent his last three decades confined at Le Quesnoy.