Born between 1180 and 1185, Theodore was a son of the "sebastokrator" John Doukas and of Zoe Doukaina. His paternal grandparents were Constantine Angelos and Theodora, a daughter of the Byzantine emperor Alexios I Komnenos (). Theodore's uncle, Andronikos, was the father of the emperors Isaac II Angelos () and Alexios III Angelos (), who were Theodore's first cousins. As with most members of his family, he preferred to use the surname of "Doukas" or "Komnenos Doukas" (Κομνηνὸς ὁ Δούκας); contemporaries variously called him "Doukas", "Komnenos", or even "Grand Komnenos" (μέγας Κομνηνός), an appellation more usually found among the ruling family of the Empire of Trebizond. Theodore evidently preferred to be associated with the more successful dynasties of the Doukai and the Komnenoi, rather than the disastrous reign of the Angeloi; indeed the only medieval writers to call him "Angelos" were the later, hostile pro-Palaiologos historians Nikephoros Gregoras and Theodore Skoutariotes, while George Akropolites refers to him as "Komnenos" until his defeat at Klokotnitsa in 1230 and as "Angelos" after.