Caradocus (middle Welsh: Karadawc) was titular king of the Britons in the absence of Emperor Magnus Maximus, who had left to campaign in Gaul according to Geoffrey of Monmouth.

Caradocus was the Duke of Cornwall during the reign of Octavius. It was he who suggested to Octavius that he should wed his daughter to Maximus and unite Britain with Rome through that union. When Octavius agreed to the idea, Caradocus sent out his son, Mauricius, to Rome as to deliver the message to Maximus. Conan Meriadoc, the king's nephew, did not approve and nearly attacked Maximus when he landed near Southampton. Only when Caradocus arrived was peace restored. They dispersed and Octavius handed Maximus the kingship and retired, as Caradocus rallied behind Maximus.

Five years after Maximus became king of Britain, he left the country to ravage the land of Gaul. He left Britain in the hands of Caradocus, who became the king unofficially. He ruled Britain for a number of years until he died and was succeeded by his brother, Dionotus.