Ambrosius Aurelianus, ; called Aurelius Ambrosius in the Historia Regum Britanniae and elsewhere, was a war leader of the Romano-British who won an important battle against the Anglo-Saxons in the 5th century, according to Gildas. He also appeared independently in the legends of the Britons, beginning with the 9th-century Historia Brittonum. Eventually he was transformed into the uncle of King Arthur, the brother of Arthur's father Uther Pendragon, and predeceases them both.