Thoma I

Mar Thoma I, also known as Valiya Mar Thoma (Mar Thoma the Great) and Arkkadiyakkon Thoma (Archdeacon Thomas) in Malayalam and Thomas de Campo in Portuguese was the first native-born, popularly-selected Metropolitan bishop of the 17th-century Malankara Church. He was the last Archdeacon of the undivided St. Thomas Christians of Malankara (Maliyankara).

After the death of Archdeacon George of the Cross on 25 July 1640, Parambil Thoma Kathanar was elected and enthroned as new Archdeacon, when he was less than 30 years old. He led the Church to the Coonan Cross Oath on 3 January 1653 and to the subsequent schism in Nasrani Church. After the Oath, he was elected as a Bishop by the Malankara (Yogam) Association and consecrated as a Bishop at St. Mary's Church Alangad, by laying hands of 12 priests on 22 May 1653. However, some factions of the community, including two Southist churches of Kaduthuruthy and Udayamperoor refused to recognise him as Bishop.

The archdeacon began to exercise powers of episcopal order, though he openly tried to regularize his episcopal consecration as a Bishop with the Church of Antioch. His episcopal consecration as a Bishop was regularized in the year 1665 by Mar Gregorios Abdal Jaleel the Patriarchal delegate of the Syriac Orthodox Patriarch of Antioch. (The exact date and place of this event is unknown). Palliveettil Mar Chandy, Kadavil Chandy Kathanar, Vengoor Geevargese Kathanar and Anjilimoottil Ittithomman Kathanar were the advisors of the bishop Mar Thoma.