Magnus I, Duke of Brunswick-Wolfenbüttel

Magnus I, called the Pious (1304–1369), was a Welf prince and the first duke to rule Brunswick-Wolfenbüttel as a principality of its own. The son of Duke Albert the Fat, he came under his brother Otto's guardianship in 1318. His wife Sophia of Brandenburg was a niece of Emperor Louis IV, who in 1333 made Magnus margrave of Landsberg.

When Otto died childless in 1344, Magnus and Ernest divided the Welf lands; Magnus took Wolfenbüttel in 1345. War with the Archbishop of Magdeburg forced him in 1347 to sell Landsberg and cede territory, and the ruined duke could not stop towns, Brunswick above all, from winning more rights.

His claims to Lüneburg helped spark the Lüneburg Succession War. In 1367 he plundered the lands of the Bishop of Hildesheim, was beaten and captured at Dinklar, and died in 1369 after paying ransom.