Theodore Angelos (Greek: Θεόδωρος Ἄγγελος, Theodōros Angelos) was co-ruler of Thessaly from ca. 1289 to his death in ca. 1299. Theodore was the third son of John I Doukas, ruler of Thessaly by his wife, who is only known by her monastic name Hypomone ("Patience"). When John died in or shortly before 1289, he was succeeded by Theodore's older brother Constantine, but Theodore served as his co-regent. Initially, the two brothers were under the tutelage of Anna Palaiologina Kantakouzene as they were underage. Awarded the title of sebastokrator in 1295, he was scheduled to marry the Armenian princess Theophano, but this project fell through. He was defeated in battle by the Byzantine general Michael Doukas Glabas Tarchaneiotes, and died in ca. 1299.