Riothamus (also spelled Riutimus or Riotimus) was a Romano-British military leader, who was active circa AD 470. He fought against the Goths in alliance with the declining Western Roman Empire. He is called "King of the Britons" by the 6th-century historian Jordanes, but the extent of his realm is unclear. Some Arthurian scholars identify Riothamus as one of the possible sources of the legendary King Arthur.