Brannes, Bremin, Brenne
An historic Gallic king who conquered Rome in the fourth century BC.
Geoffrey of Monmouth expands his legend, saying that he was the son of King Dunwallo of Britain and the brother of Belinus. Brennius and Belinus went to war after their father's death, and Brennius was defeated. Retreating to Gaul, he became the duke of Burgundy.
Eventually, the brothers were reconciled and, together, they conquered Gaul and Rome. Brennius stayed to rule Rome while Belinus returned to Britain.
Brennius may be reflected in the Welsh character Bran.