Otto I of Brunswick-Lüneburg, a member of the House of Welf, was the first duke of Brunswick-Lüneburg from 1235 until his death. He is called Otto the Child to distinguish him from his uncle, Emperor Otto IV.

The House of Welf is a European dynasty that has included many German and British monarchs from the 11th to 20th century and Emperor Ivan VI of Russia in the 18th century. The originally Franconian family from the Meuse-Moselle area was closely related to the imperial family of the Carolingians.