Феодор Комнин Дука
Born , Demetrios was the younger son of Theodore Komnenos Doukas and Maria Petraliphaina. As such he was a great-grandson of the Byzantine emperor Alexios I Komnenos () and Empress Irene Doukaina, and first cousin once removed of the emperors Isaac II Angelos () and Alexios III Angelos (), sharing descent from Constantine Angelos, the founder of the Angelos lineage. Unlike his father and most of his relatives, who eschewed the surname of "Angelos" due to the disastrous reigns of the Angelid emperors, and preferred to use the more prestigious surnames of "Doukas" or "Komnenos", Demetrios used the name "Angelos Doukas" (Ἀγγελοδούκας) in a manuscript notice dated 25 September 1244.