Dagobert I (dăg´ōbûrt), c.612–c.639, Frankish king, son and successor of King Clotaire II. His father was forced to appoint Dagobert king of the East Frankish kingdom of Austrasia at the request of Pepin of Landen, mayor of the palace, and Arnulf, bishop of Metz, who effectively ruled in Austrasia. After Clotaire's death (629) Dagobert reunited Aquitaine with Austrasia and Neustria and became king of all the Franks. He was, however, forced by popular demand to give (634) Austrasia its own king in the person of his son, Sigebert III. The last of the Merovingians to exercise personal rule, he made himself independent of the great nobles, especially of Pepin of Landen. He extended his rule over the Basques and the Bretons. Dagobert's reign was prosperous; he was a patron of learning and the arts. He founded the first great abbey of Saint-Denis, where he is buried.