Greek emperor of Nicaea, A. D. 1206-1222, was descended from a noble family at Constantinople. While in a private station he married Anna Angela Comnena, the second daughter of the emperor Alexis III. Angelus. He was a man of energy and ability. and exhorted his father-in-law to resist the Latins when they laid siege to Constantinople in 1203, ; but Alexis in despair abandoned the city and fled to Italy, to Conrad, Marquis of Monteferrato, who had married his sister. In the troubles which followed at Constantinople, the history of which has been related elsewhere [ALEXIS IV. and V.], Theodore continued to support the party that was opposed to the Latins; but after Constantinople had been taken by storm on the 12th of April 1204, and Baldwin, count of Flanders, had been placed on the imperial throne, Theodore fled with his wife to the Asiatic coast. Here he succeeded in raising some troops, by means of which he made himself master of the town of Nicaea, and the greater part of Bithynia. He was, however, soon deprived of his conquests by Louis Count of Blois, who had received Bithynia as his share of the Byzantine dominions; but he recovered them again when Louis was recalled' to Constantinople to the assistance of Baldwin, who was hard pressed by the Bulgarians and the revolted Greeks. Theodore had previously governed with the title of Despot, in the name of his father-hi-law, the deposed emperor Alexis II.; but as the latter was. still retained in captivity by the Marquis of Monteferrato, he now assumed the title of emperor of the Romans, as lawful heir to the crown, in virtue of his marriage with Anna, and was publicly crowned at Nicaea as emperor by Michael Autorianus, the Greek patriarch (1206). His title, however, was disputed by several other Greek princes, who had established for themselves independent principalities in Asia Minor. The most formidable of these rivals was Alexis Comnenus, who reigned as emperor at Trebizond, with whom Theodore carried on a successful war for some years. He also had to contend with Henry, the Latin emperor at Constantinople, and the successor of Baldwin, over whom he gained several victories ; and it is no small proof of his abilities, that although surrounded by so many enemies, he gradually extended his dominions, and increased his power. For the history of his war with the Latins, see HENRICUS. In 1210 a new enemy appeared. In this year his father-in-law, Alexis, who had escaped from captivity, claimed the throne, and was supported in his claims by Gayáth-ed-dín, the powerful sultan of Koniah. As Theodore refused to surrender the crown to his father-in-law, the sultan marched against him at the head of a powerful army, but was defeated and slain in battle. Alexis fell into the hands of Theodore, who kept him in confinement in a monastery, where he died some years afterwards. Theodore spent the latter years of his reign in peace. He died in 1222, a little more than 45 years of age, and in the 18th year of his reign, computing from the time that he first became master of Nicaea, but in the 16th year from the date of his coronation. He left no male offspring, and was succeeded by his son-in-law Joannes Vatatzes, who had married his daughter Irene [JOANNES III.]. Theodore was married thrice. 1. To Anna Comnena, the daughter of Alexis III. '2. To Philippa, an Armenian princess, whom he divorced. 3. To Maria, the daughter of Peter of Courtenay, emperor of Constantinople. (Nicetas, Alex. Comn. and Balduinus ; Acropolita, cc. 6, 14, 15, 18 ; Du Cange, Familiae Byzantinae, p. 219.)