Magnus I (1304–1369), called the Pious (Latin Pius), was a notable German noble from the House of Welf, a powerful dynasty in medieval Germany.
Magnus was a key figure in the Welf dynasty’s efforts to consolidate their territorial holdings during a time of political fragmentation in the Holy Roman Empire.
When Otto died in 1344, Magnus and Ernest jointly took over government of the state; but already on 17 April 1345, they agreed to divide the territory.
In exchange for help in this conflict, Magnus sold the Margraviate of Landsberg to Frederick II, Margrave of Meißen.
The prince of Lüneburg, William II, Duke of Brunswick-Lüneburg, a member of the same house to which Magnus belonged, the House of Welf, did not have sons; however, he had already promised the principality to a son of his daughter, a relative of the Duke of Saxony, before he agreed to Magnus' plan.