Thoma I

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

Following the death of Archdeacon George of the Cross on 25 July 1640, Parambil Thoma Kathanar was elected and enthroned as the new Archdeacon while still under 30 years old. He played a significant role in leading the Church during the Coonan Cross Oath on 3 January 1653, an event that led to a schism within the Nasrani Church. After the Oath, Thoma was elected as a Bishop by the Malankara Yogam (Association) and was consecrated at St. Mary's Church, Alangad, by the laying on of hands by 12 priests on 22 May 1653. However, certain factions within the community, including two Southist churches in Kaduthuruthy and Udayamperoor, did not recognize his episcopal authority.

Despite this, Thoma began to exercise episcopal powers and sought to regularize his consecration with the Church of Antioch. His episcopal consecration was formally recognized in 1665 by Mar Gregorios Abdal Jaleel, a delegate of the Syriac Orthodox Patriarch of Antioch, though the exact date and location of this event remain unknown. During his tenure, Mar Thoma was advised by Palliveettil Mar Chandy, Kadavil Chandy Kathanar, Vengoor Geevargese Kathanar, and Anjilimoottil Ittithomman Kathanar.