William of Brunswick-Grubenhagen

William of Brunswick-Grubenhagen (c. 1298–1360) was the third son of Henry I the Miraculous and Agnes of Meissen. On his father's death in 1322 he ruled the Principality of Grubenhagen with his brothers Henry II and Ernest I.

The brothers soon divided most of the land, though a 1324 pact kept their chief towns in common. William reigned until his death in 1360; childless, he was succeeded by his brother Ernest I, who united the whole principality.