William IV, Duke of Brunswick Lüneburg

William (German: Wilhelm) called William the Younger (German: Wilhelm der Jüngere, c. 1425 – 7 July 1503) was duke of Brunswick-Lüneburg and ruled over the Wolfenbüttel and Göttingen principalities.

The eldest son of William the Victorious, Duke of Brunswick-Lüneburg, he was given the Principality of Göttingen by his father in 1473. In 1482 the father died, and he and his brother Frederick succeeded their father in the remaining parts of his state; however, William had Frederick imprisoned in 1484 and made himself sole ruler. In 1490 he bought the City of Helmstedt from the Abbott of Werden. In 1491, William gave the Principality of Wolfenbüttel including Calenberg to his sons, and kept only Göttingen to himself. In 1495 he resigned as prince of Göttingen in favour of his son Eric I in return for an appanage. William died on 7 July 1503 in Hardegsen.