Ambrosius Aurelianus

Ambrosius Aurelianus (Welsh, Emrys Wledig); 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.

http://en.wikipedia.org/wiki/Ambrosius_Aurelianus