The following article is excerpted from the International Standard Bible Encyclopedia, which is in the public domain.
In the New Testament
One of the Twelve Apostles. Thomas, who was also called "Didymus" or "the Twin" (compare John 11:16; 20:24; 21:2), is referred to in detail by the Gospel of John alone. His election to the Twelve is recorded in Matthew 10:3; Mark 3:18; Luke 6:15; Acts 1:13. In John 11:1-54, when Jesus, despite imminent danger at the hands of hostile Jews, declared His intention of going to Bethany to heal Lazarus, Thomas alone opposed the other disciples who sought to dissuade Him, and protested, "Let us also go; that we may died with him" (John 11:16). On the eve of the Passion, Thomas put the question, "Lord, we know now whither thou goest; how know we the way?" (John 14:5).
After the crucifixion, Thomas apparently severed his connection with the rest of the apostiles for a time, as he was not present when the risen Christ first appeared to them (compare John 20:24). But his subsequent conversation with them, while not convincing him of the truth of the resurrection--"except I shall see .... I will not believe" (John 20:25)--at least induced him to be among their number eight days afterward (John 20:26) in the upper room. There, having received the proofs for which he sought, he made the confession, "My Lord and my God" (John 20:28), and was reproved by Jesus for his previous unbelief: "Because thou hast seen me thou hast believed: blessed are they that have not seen, and yet have believed" (John 20:29). He was one of the disciples to whom Jesus manifested Himself during the fishing expedition at the Sea of Tiberias (John 21:1-11).
In Apocryphal Literature
According to the "Genealogies of the Twelve Apostles" (compare Budge, The Contendings of the Apostles, II, 50), Thomas was of the house of Asher. The oldest accounts are to the effect that he died a natural death of (compare Clement of Alexandria iv.9, 71). Two fields are mentioned by apocryphal literature as the scene of Thomas' missionary labors.
(1) According to origen, he preached in Parthia, the according to a Syrian legend he died at Edessa. The Agbar legend also indicates the connection of Thomas with Edessa. But Eusebius indicates it was Thaddaeus and not Thomas who preached there (see THADDAEUS).
(2) Along with these are other sources identifying Thomas with India.
Thus, "The Ac of Thomas" (see APOCRYPHAL ACTS, sec. B, V), a Gnostic work dating from the 2nd century, tells how when the world was partitioned out as a mission field among the disciples, India fell to "Judas Thomas, also called Didymus," and narrates his adventures on the way, his trials, missionary success, and death at the hands of Misdai, king of India (compare Budge, II, 404; Hennecke, Neutestamentliche Apokryphen, 473-544; Pick, The Apocryphal Acts, 224). The "Preaching of Thomas" (compare Budge, II, 319) relates still more fantastic adventures of Thomas in India, and the "Martyrdom of Thomas in India" states that on his departure toward Macedonia he was put to death as a sorcerer. Of the two, the former is the more probable.
An attempt at reconciliation has been made by supposing that the relics of Thomas were transported from India to Edessa, but this is based on inaccurate historical information (compare Hennecke, op. cit., 474). The additional names "Judas" and "Didymus" have causd further confusion in apocryphal literature in regard to Thomas, and have led to his identification with Judas of James, and hence, with Thaddaeus (see THADDAEUS), and also with Judas the brother of Jesus (compare Matthew 13:55). Thus in the "Ac of Thomas" he is twice called the "twin brother of the Messiah." Another legend makes Lysia the twin sister of Thomas. A Gnostic "Gospel of Thomas" (see APOCRYPHAL GOSPELS, III, 2, (a)) was known to Irenaeus (compare Irenaeus, Adv. Haer., 1,20).
Although little is recorded of Thomas in the Gospels, he is yet one of the most fascinating of the apostles. He is typical of that nature--a nature by no means rare--which contains within it certain conflicting elements exceedingly difficult of reconciliation. Possessed of little natural buoyancy of spirit, and inclined to look upon life with the eyes of gloom or despondency, Thomas was yet a man of indomitable courage and entire unselfishness. Thus with a perplexed faith in the teaching of Jesus was mingled a sincere love for Jesus the teacher. In the incident of Christ's departure for Bethany, his devotion to his Master proved stronger than his fear of death.
Thus far, in a situation demanding immediate action, the faith of Thomas triumphed; but when it came into conflict with his standards of belief it was put to a harder test. For Thomas desired to test all truth by the evidence of his senses, and in this, coupled with a mind tenacious both of its beliefs and disbeliefs, lay the real source of his religious difficulties. It was his sincerity which made him to stand aloof from the rest of the disciples till he had attained to personal conviction regarding the resurrection; but his sincerity also drew from him the testimony to that conviction, "My Lord and my God," the greatest and fullest in all Christianity.
International Standard Bible Encyclopedia