Catholicos Aboon Mor Baselios Thomas-I,the spiritual head of the Syrian Christians of India,was born in the Cheruvillil family of Vadayambadi, Puthenkuriz to Mathai and Kunjamma on 22nd July 1929.
His priestly formation was under the guidance of Mor Philoxenos Paulose (late Catholicos Mor Baselios Paulose-II) who ordained him ‘Korooyo’ in 1952 and ‘Shamshono’ at Kadamattom Church in 1957. In August 1958, C M Thomas was ordained ‘Kassisso’ (full priest) by Mor Yulius Elias at the Majanikkara Dayro.
In 1959 he was appointed as the vicar of St.Peter’s church, Puthencuriz. Later he served the churches at Vellathooval, Keezhumuri, Fort Cochin, Valamboor, Calcutta and Thrissur. For a period of seven years from 1967, he was the organizing secretary of Kolenchery Medical Mission Hospital. He also served as the Chief organizer of the North Indian mission at Bhilai in 1970’s and as the secretary of the Pourasthaya Suvishesha Samajam in 1974. He was well known as a great revivalist preacher and was also recognized as an excellent organizer.
In January 1974, Fr. C M Thomas was elected to the episcopate by the Malankara Jacobite Syrian Christian Association convened at the Karingachira St. George Church and was consecrated Metropolitan with the title ‘Mor Dionysius’ by H.H. Mor Ignatius Ya`qub-III on 24th February 1974 at Damascus, Syria. He was entrusted with the charge of Angamali diocese, the largest of all the Syrian Orthodox dioceses which has a membership of more than half a million.
On Friday the 26th July 2002, His Holiness Moran Mor Ignatius Zakka-I Iwas the Patriarch of Antioch & all the East, consecrated the 73-year old Mor Dionysius Thomas as the CATHOLICOS with the title ‘BASELIOS THOMAS I’ at a solemn function held at the St. Peter & St. Paul Cathedral in Mor Ephrem Monastery, Ma`arat Sayyidnaya, near Damascus.
In the Syrian Orthodox Church hierarchy, the Catholicos is second in rank to the supreme spiritual head, the Patriarch of Antioch.