An early king of Britain (c. fifth century BC) in Geoffrey of Monmouth. He was the son of King Cloten of Cornwall. When he was born, Britain was fragmented, having crumbled after the death of Porrex.

Dunwallo conquered King Pinnier of England, King Ruduac of Wales, and King Stater of Scotland, unifying the island of Britain again. In his forty years on the throne, he established law, order, and justice. When he died, his sons, Belinus and Brennius, contended for the kingdom.

According to the fourteenth-century Short Metrical Chronicle, which has a confused chronology, Merlin served Dunwallo and built Stonehenge in his honor.