Ambrosius Aurelianus
Many historical personas (some already included in the Arthurian legend) exist in the cycle, alongside less "factual" characters: Taliesin, Magnus Maximus, Theodosius, Ambrosius Aurelianus, Vortigern, Constantine III, Myrddin Wyllt, Clovis I, Gwyddno Garanhir, Elffin ap Gwyddno, Horsa, Hengest, Cerdic, Aelle, Gildas, and Aneirin (in the series, it is revealed that the last two are the same person; born with the name Aneirin, he changes it to Gildas after Arthur's death).