Despot and first emperor of Nicaea (1204-1222) after the overthrow of the Byzantine Empire by the Fourth Crusade (1202-1204).
While still a member of the Byzantine aristocracy, Theodore married Anna, second daughter of Emperor Alex- ios III Angelos (1199). After the Latin conquest of Constantinople in 1204, he fled with his wife and children to Nicaea (mod. Iznik, Turkey), where he was acknowledged by the locals as their ruler as early as fall 1204. First using the title of despot, he was crowned as “emperor of the Romans” in 1208, shortly after the election of the first patriarch of Constantinople in exile. Theodore seems to have shown an interest in the negotiations between representatives of the Greek Orthodox and the Latin churches, and in 1214 he took an active role in the talks that took place in the Nicaean Empire. He was unsuccessful in most of his military encounters with the Franks of the newly established Latin Empire of Constantinople and with the Venetians, but in 1211 he successfully repelled a Turkish invasion.
In the late 1210s, Theodore was able to establish a close relationship with the ruling family of Constantinople by marrying Maria, sister of Emperor Robert, and by planning to marry his own daughter Eudokia to Robert, in spite of fierce opposition by the ecumenical patriarch. He also offered Venice trading privileges, which were to last for five years, in 1219. Theodore seems to have died without a male heir and was buried in the monastery of Hyakinthos in Nicaea. He was succeeded by his son-in-law, John III Vatatzes.