Coilus was a legendary king of the Britons during the time of the Roman occupation of Britain as recounted in Geoffrey of Monmouth's pseudohistorical Historia Regum Britanniae. He came to power in 142AD.^[1]

He was the son of King Marius and ruled following his father's death.

According to Geoffrey, Coilus was brought up in Rome and favoured the company of Romans in Britain.^[2] Throughout his reign, he paid Rome its tribute without question. In Britain, he allowed the nobles peace and granted them large gifts. He was succeeded by his only son, Lucius.