Thomas the Apostle (called Didymus which means "the twin") was one of the Twelve Apostles of Jesus Christ, according to the New Testament. He is informally called doubting Thomas because he doubted Jesus' resurrection when first told, (in the Gospel of John), followed later by his confession of faith, "My Lord and my God", on seeing Jesus' wounded body.
Traditionally, he is said to have travelled outside the Roman Empire to preach the Gospel, travelling as far as India. According to tradition, the Apostle reached Muziris, India in AD 52 and baptized several people, founding what today are known as Saint Thomas Christians or Nasranis. After his death, the reputed relics of Saint Thomas the Apostle were enshrined as far as Mesopotamia in the 3rd century, and later moved to various places. In 1258, some of the relics were brought to Abruzzo in Ortona, Italy, where they have been held in the Church of Saint Thomas the Apostle. He is often regarded as the Patron Saint of India, and the name Thoma remains quite popular among Saint Thomas Christians of India. Thomas first speaks in the Gospel of John. In John 11:16, when Lazarus had recently died, the apostles do not wish to go back to Judea, where some Jews had attempted to stone Jesus. Thomas says: "Let us also go, that we may die with him
He speaks again in John 14:5. There, Jesus had just explained that he was going away to prepare a heavenly home for his followers, and that one day they would join him there. Thomas reacted by saying, "Lord, we don't know where you are going, so how can we know the way?"
John 20:24-29 tells how doubting Thomas was skeptical at first when he heard that Jesus had risen from the dead and appeared to the other apostles, saying, "Except I shall see in his hands the print of the nails, and put my finger into the print of the nails, and thrust my hand into his side, I will not believe." (v.25) But when Jesus appeared later and invited Thomas to touch his wounds and behold him, Thomas showed his belief by saying, "My Lord and my God". Jesus then said, "Thomas, because thou hast seen me, thou hast believed: blessed [are] they that have not seen, and [yet] have believed."
When the feast of Saint Thomas was inserted in the Roman calendar in the 9th century, it was assigned to 21 December. The Martyrology of St. Jerome mentioned the apostle on 3 July, the date to which the Roman celebration was transferred in 1969, so that it would no longer interfere with the major ferial days of Advent. 3 July was the day on which his relics were translated from Mylapore, a place along the coast of the Marina Beach, Chennai (Madras) in India, to the city of Edessa in Mesopotamia. Traditionalist Roman Catholics (who follow the General Roman Calendar of 1960 or earlier) and many Anglicans (including members of the Episcopal Church as well as members of the Church of England and the Lutheran Church, who worship according to the 1662 edition of the Book of Common Prayer), still celebrate his feast day on 21 December.
The Eastern Orthodox and Byzantine Catholic churches celebrate his feast day on 6 October (for those churches which follow the traditional Julian Calendar, 6 October currently falls on 19 October of the modern Gregorian Calendar). In addition, the next Sunday of the Easter (Pascha) is celebrated as the Sunday of Thomas, in commemoration of Thomas' question to Jesus, which led him to proclaim, according to Orthodox teaching, two natures of Jesus, both human and divine. Thomas is commemorated in common with all of the other apostles on 30 June July), in a feast called the Synaxis of the Holy Apostles. He is also associated with the "Arabian" (or "Arapet") icon of the Theotokos (Mother of God), which is commemorated on 6 September (19 September). The Malankara Orthodox church celebrates his feast on three days, 3 July (in memory of the relic translation to Edessa), 18 December (the Day he was lanced)  and 21 December (when he died)