William I, Duke of Bavaria-Straubing (Frankfurt am Main, May 12, 1330 – April 15, 1389, Le Quesnoy), is the second son of the emperor Louis IV the Bavarian from his second wife Margaret of Holland and Hainaut.

He is also known as William V, Count of Holland, as William III, Count of Hainaut and as William IV, Count of Zeeland.