Person

Thomas the Apostle

One of the Twelve apostles, named first in the four apostolic lists as Thōmas (Aramaic t'ōmā, "twin") and equivalently Didymos (Greek "twin"), prominent in John's Gospel for both his loyalty ("let us also go, that we may die with Him," John 11:16) and his resurrection-skepticism-resolved confession ("My Lord and my God!" John 20:28). According to strong and continuous tradition, Thomas evangelized Parthia and India, planted the seven Saint Thomas churches of Kerala (~AD 52), and was martyred at Mylapore (modern Chennai) ~AD 72.

Biographical sketch

Name and origin: "Thomas" and "Didymus" both mean "twin." No biological twin is named in the canonical record (some apocryphal Acts of Thomas tradition makes him Jesus's twin, which the canonical tradition rejects). Likely Galilean, though origin is not specified.
Listed among the Twelve: Matt 10:3; Mark 3:18; Luke 6:15; Acts 1:13.
Distinctive Johannine scenes:
Lazarus episode (John 11:16): when Jesus resolves to go back to Judea despite the threat from authorities, Thomas says to the others, "Let us also go, that we may die with Him." A model of resolute loyalty.
Way, truth, and life (John 14:5): Thomas's question "Lord, we do not know where You are going; how do we know the way?" prompts Jesus's "I am the way, the truth, and the life" (John 14:6), one of the most-cited Christological texts.
Doubt and confession (John 20:24-29): absent on Easter evening; refuses to believe without seeing the wounds; eight days later Jesus appears, invites Thomas to touch the wounds, and Thomas confesses "My Lord and my God!" (ho Kyrios mou kai ho Theos mou), the climactic Christological confession of the Fourth Gospel and one of the strongest NT affirmations of Jesus's deity.
Post-resurrection appearance (John 21:2): present at the Galilean lakeside breakfast with seven other disciples.

"My Lord and my God", theological significance

The confession in John 20:28 is the climax of the Fourth Gospel's Christology. Thomas addresses the risen Jesus directly with ho Kyrios mou kai ho Theos mou, both nouns articular and predicated of Jesus. Jesus does not correct the language (compare Acts 14:14-15; Rev 19:10; 22:9, where Paul and the angel sharply correct misdirected worship). The acceptance of Theos applied to Himself is one of the clearest NT self-attestations of Jesus's deity, and the verse is foundational for Christs Deity arguments. The unitarian / Jehovah's Witness reading (Thomas was "exclaiming to God in surprise") fails grammatically (the autōi, "to him", anchors the address to Jesus).

Post-resurrection ministry

The canonical Acts does not narrate Thomas's later mission. Patristic and Indian-traditional sources fill in:

Parthia (per Eusebius of Caesarea HE 3.1, citing Origen): Thomas was allotted Parthia. Parthia is a broad term that historically encompassed Mesopotamia and the trade routes east to India.
India (per Coptic tradition, Ephrem the Syrian, the Acts of Thomas tradition, and the continuous Saint Thomas Christians of Kerala): Thomas arrived in Kerala (Malabar coast) ~AD 52; founded seven churches (Cranganore, Palayoor, Kottakkavu, Kokkamangalam, Niranam, Nilackal, Kollam); preached at the court of King Gondophares (Indo-Parthian, AD 19-46, attested by coins). Eventually moved east to Tamil Nadu and was speared to death at Mylapore (modern Chennai), ~AD 72.
Historical assessment: The India tradition is the strongest non-canonical apostolic-mission tradition, supported by:
Continuous Christian community in Kerala from at least the 6th century (Cosmas Indicopleustes attests it as an established, Persian-bishop-connected church)
Coin discoveries (1834+) confirming Gondophares's historicity (he was thought legendary until then)
Ancient Mediterranean-India trade routes (the Periplus of the Erythraean Sea, c. AD 60, documents heavy commercial traffic)
Independent Christian community using Syriac (not Latin/Greek) liturgy, indicating early Eastern provenance
Tomb: traditional site at Mylapore (now Chennai); relics later translated to Edessa, then to Ortona, Italy.

Theological themes

Faith and evidence: the Thomas episode (John 20:24-29) is the canonical NT meditation on faith and evidence. Jesus does not rebuke Thomas for wanting evidence; He grants the evidence. But the beatitude that follows, "blessed are they who did not see, and yet believed", frames future Christian faith as believing without the wound-touching access Thomas got, on the testimony of those who did see. Foundational for faith-and-reason / Apologetics discussion.
Resurrection apologetics: Thomas's skepticism-resolved-by-evidence is part of the NT's internal apologetic against the they-just-believed-because-they-wanted-to objection.
Christ's deity: as above, John 20:28 is one of the strongest Christological texts.
Loyalty under threat: the Lazarus episode (John 11:16) shows Thomas's costly loyalty.