Otto III, Duke of Brunswick-Lüneburg

Otto III (c. 1296–1352) of the House of Welf, the second son of Otto the Strict and Matilda of Bavaria, was Prince of Lüneburg from 1330. In 1315 his father arranged the succession of Otto and his brother William II, and from 1330 the brothers ruled the undivided land together.

They enlarged their estates around Gifhorn and backed the growing towns, making the Ilmenau navigable between Lüneburg and Uelzen, so that Lüneburg's trade flourished.

The Ilmenau also took Otto's only son, who drowned in it as a child. When Otto died in 1352 he left no male heir, leaving William to face the succession question that ended in war after William's death.