John X Kamateros was the Patriarch of Constantinople from 1198 to 1206. He fled to Thrace with the deposed emperor Alexios III Angelos after the capture of Constantinople during the Fourth Crusade in 1204. In 1206, Theodore I Laskaris invited him to Nicaea where Theodore founded the Byzantine successor state of the Empire of Nicaea, but John died in the same year. The Crusaders installed a Latin Patriarch in Constantinople, while Theodore simply created a new Greek Patriarchate in Nicaea, which was eventually restored in Constantinople with the rest of the Empire in 1261.