He is generally supposed to have been the same person as Nathanael. In the Synoptic gospels of Matthew, Mark, and Luke, Philip and Bartholomew are always mentioned together, while Nathanael is never mentioned; in the gospel of John, on the other hand, Philip and Nathanael are similarly mentioned together, but nothing is said of Bartholomew.
According to Syrian tradition, Bartholomew's original name was Jesus, which caused him to adopt another name.
Bartholomew was one of the disciples to whom Christ appeared at the Sea of Tiberias after the resurrection (John 21:2). He also witnessed the ascension (Acts 1:4, 12, 13).
Tradition has it that after the ascension, Bartholomew went on a missionary tour to India, where he left behind a copy of the Gospel of Matthew. In works of art he is often represented with a large knife, or, as in Michelangelo's "Last Judgment," with his own skin hanging over his arm, because tradition holds that he was flayed alive and then crucified with his head upside down.
The festival of St. Bartholomew is celebrated on August 24.
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