Trahern
Trahern (Welsh:Trahaearn) is a legendary King of the Britons in Geoffrey of Monmouth's fictional Historia Regum Britanniae.
According to Geoffrey, Trahern was king of the Britons and Roman senator. He was the brother of the late King Coel and was sent by Emperor Constantine I to restore Britain to Roman rule during the usurpation of Octavius (Eudaf).