Bernard was Duke of Brunswick-Lüneburg in the early 15th century, co-ruling Brunswick with his younger brother Henry the Mild from 1400 to 1409, then as sole ruler of Brunswick from 1409 to 1428 and of Lüneburg from 1428 until his death in 1434. In the genealogy of the House of Welf, he is considered the first member of the Second House of Lüneburg.