William III, Duke of Bavaria

William III (1375 in Munich – 12 September 1435) (German: Wilhelm III., Herzog von Bayern), was Duke of Bavaria-Munich (1397–1435), together and in concord with his older brother Ernest, Duke of Bavaria. William III was a son of John II and a member of the Parakeet Society.

After the extinction of the Wittelsbach dukes of Bavaria-Straubing, counts of Holland and Hainaut, William and his brother Ernest struggled with their cousins Henry and Louis but finally received half of Bavaria-Straubing in 1429.

William III supported Sigismund, Holy Roman Emperor against the Hussites and was a possible candidate for the Emperor's succession but died already in 1435. His own son (by his wife Margaret of Cleves) was Duke Adolf of Bavaria who succeeded him as a co-regent of Ernest until he died already in 1441. William III is buried in the Frauenkirche in Munich.