Person

Bartholomew the Apostle

One of the Twelve apostles, almost universally identified by patristic tradition with Nathanael of John's Gospel (John 1:45-51; 21:2). The name Bartholomew (Aramaic bar-Tolmai, "son of Tolmai") is a patronymic; Nathanael would be his given name. According to strong tradition, Bartholomew evangelized Armenia (with Jude Thaddaeus) and parts of India, and was martyred in Armenia by being flayed alive then beheaded ~AD 68, making him a co-founder of the Armenian Apostolic Church.

Biographical sketch

Name identification: the Synoptics list "Bartholomew" alongside Philip in the apostolic lists (Matt 10:3; Mark 3:18; Luke 6:14; Acts 1:13) without naming Nathanael; John names "Nathanael" alongside Philip (John 1:45-51) without naming Bartholomew. Patristic tradition (Augustine doubted, but the majority view from the 9th c. onward) identifies them as the same person. The pairing with Philip in both traditions is the strongest evidence.
Origin: Cana of Galilee (John 21:2, "Nathanael of Cana of Galilee").
Calling (John 1:45-51): Philip found Nathanael and said "We have found him of whom Moses in the Law and the prophets wrote, Jesus of Nazareth." Nathanael's famous reply: "Can any good thing come out of Nazareth?" Philip's response: "Come and see." Upon meeting Jesus, Nathanael was confronted with Jesus's prior knowledge of him ("when you were under the fig tree, I saw you") and confessed: "Rabbi, You are the Son of God; You are the King of Israel!" Jesus then prophesied that Nathanael would see "the heavens opened and the angels of God ascending and descending on the Son of Man", a Jacob-ladder reference (Gen 28:12) identifying Jesus as the true Bethel.
Among the Twelve: listed in all four apostolic lists, usually paired with Philip.
Post-resurrection: John 21:2 places Nathanael among the seven disciples at the Galilean lakeside breakfast.

"An Israelite indeed, in whom there is no deceit"

Jesus's characterization of Nathanael at first meeting (John 1:47), alēthōs Israēlitēs en hō dolos ouk estin, is the only Gospel instance of Jesus paying a positive character-assessment compliment of this form. The contrast with Jacob ("Israel"), who was characterized by dolos (deceit, Gen 27:35), is theological, Nathanael is a true Israelite where the patriarch was deceitful. The fig-tree reference further connects to Israelite identity (Mic 4:4; Zech 3:10).

Post-resurrection ministry

The canonical Acts does not narrate Bartholomew's later mission. Patristic tradition fills in:

Armenia (per uniform tradition, esp. Movses Khorenatsi's 5th-c. History of Armenia): Bartholomew preached in Armenia AD 60-68, eventually martyred at Albanopolis (uncertain location, possibly modern Başkale in eastern Turkey) by being flayed alive and beheaded. The flaying iconography (Michelangelo's Last Judgment shows Bartholomew holding his own skin) is medieval-traditional.
India (per Eusebius of Caesarea HE 5.10): Eusebius reports that the Christian philosopher Pantaenus of Alexandria, sent on mission to India ~AD 180, found Christian communities there using a Hebrew Matthew left by Bartholomew. This is the canonical patristic basis for Bartholomew's India mission. The "India" of Eusebius is geographically vague but at minimum implies the southern Arabian peninsula or western India.
Confidence level: Armenia is the strongest tradition; India is patristic but late.

Co-founder of the Armenian Church

Together with Jude Thaddaeus, Bartholomew is one of the two apostles traditionally credited with the founding of Armenian Christianity. The Armenian Apostolic Church regards both as co-founders ("first illuminators of Armenia," with Gregory the Illuminator as second / decisive illuminator in AD 301). Armenian iconography typically depicts Bartholomew with a flaying knife.

Theological themes

The honest seeker: Nathanael's question "Can any good thing come out of Nazareth?" is honest skepticism, not malicious unbelief. Philip's "come and see" is a model of inviting investigation rather than demanding immediate assent. This is a classic apologetic-tactic text.
Christ as the true Bethel: Jesus's Jacob-ladder reference (John 1:51) identifies Jesus Himself as the meeting-place of heaven and earth, a theme deepened in John's Gospel (the naos of the body, John 2:21; the temple imagery).
Witness through suffering: the flaying tradition makes Bartholomew a paradigm of extreme apostolic martyrdom; his association with Armenia ties this to one of Christianity's most-persecuted historical communities (see the Armenian Genocide, treated in Armenian Apostolic Church).