Identity: Bartholomew and Nathanael
Bartholomew appears in all three Synoptic apostolic lists (Matthew 10:3, Mark 3:18, Luke 6:14) always paired immediately with Philip, but never appears at all in John's Gospel — where instead a figure named Nathanael is introduced by Philip to Jesus (John 1:45–51) and receives one of the Gospels' more striking commendations: Jesus calls him "an Israelite indeed, in whom there is no guile" before Nathanael has said a word to identify himself, prompting Nathanael's own confession, "Rabbi, you are the Son of God, you are the King of Israel." "Bar-tholomew" is itself a patronymic ("son of Tolmai/Talmai"), not a given name, which is part of why most scholars conclude Bartholomew and Nathanael are the same person under two different names — the Synoptics using his patronymic, John using his personal name, similar to how Simon and Peter both refer to the same apostle.
Later ministry and martyrdom tradition
Church tradition, with real diversity in the specific details, holds that Bartholomew carried the gospel eastward — variously to Armenia, India, and Mesopotamia, with Armenian tradition especially strong: alongside Thaddeus, Bartholomew is honored as a co-founder of the Armenian Apostolic Church, and Armenia's claim to be the first officially Christian nation (early fourth century) draws directly on this apostolic-founding tradition. His martyrdom is traditionally located in Armenia, and the specific manner — being flayed alive and then beheaded — became his standard iconographic identifier, which is why Bartholomew is typically depicted in religious art holding his own skin or a flaying knife (most famously in Michelangelo's Last Judgment, where Michelangelo controversially painted his own face onto Bartholomew's flayed skin). As with several of the Twelve, the specific manner of death has multiple, not fully reconcilable, ancient traditions, but the location (Armenia) and general manner (a violent martyrdom) are consistently attested across sources.
Why it matters
Bartholomew/Nathanael's brief but vivid scene in John — being seen and known by Jesus before any words are exchanged — is worth returning to on its own terms: it's one of the New Testament's clearest small pictures of what it means to be truly known by Christ before you've said anything to explain or justify yourself.