Catholicos (Greek καθολικός, pl καθολικοί, as a whole, general, universal, . Latinized catholicus ) is an ecclesiastical title, which was worn by the bishop of Seleucia- Ctesiphon since the 4th century. The function and position essentially corresponds to that of a patriarch.

The Bishop of Seleucia- Ctesiphon was equated as head of the Church in the Persian Empire under the pseudo- Nicene Canons of the five patriarchs. Since the Sassanid Empire with Ostrom was in a permanent state of stress (see Late Antiquity and the Roman -Persian Wars), the contact between the Church in Persia and the Roman imperial church were disabled. Moreover, it was not possible against the authorities, that a subject of the Emperor's representative of the Christians was. The Catholicos was given the right to appoint subordinate bishops in their own right and to be elected by them, but remained under the supervision of the Patriarch of Antioch.

After 483 the Persian Church declared at the synod of Beth- Lapat as Catholicos of the East, the teachings of Nestorius for binding, the Catholicos of the East added to his title to the title of patriarch.

The Syriac Orthodox Patriarch of Antioch appointed at a later period a Catholicos ( Maphrian ) as deputy to the east, who resided in Takrit in Iraq in the Middle Ages. Of these, the Katholikate the Malankara Syriac Orthodox Church and the Malankara Orthodox Syrian Church lead (Indian Orthodox Church) ago ( " Catholicos of the East" or " Catholicos of India ").

For similar political reasons, the leaders of the Armenian Apostolic Church and of Albania in the Caucasus and the Georgian Church received the Katholikostitel in the Middle Ages. The Armenian Church has both patriarchs and catholicoi; Patriarchs are here rank among the catholicoi.

Also, some heads with Rome united churches use the title of Catholicos, the Armenian Catholic Patriarch and the Major Archbishop of the Syro- Karen.