The Gospels of Matthew, Mark, and Luke and the Acts of the Apostles count Bartholomew as one of the 12 apostles, associating his name Philip. John’s Gospel links the name Nathaniel with Philip and never mentions Bartholomew. Apart from that, we know little about him.
Some scholars identify the apostle Bartholomew with Nathaniel, a solution supported by the fact that Bartholomew could be a surname (‘bar Tolomai’, son of Tolomai) and Nathaniel a given name: Nathaniel Bartholomew. If so, then Nathaniel was the man in whom the Lord saw ‘no guile’ and one who was among the apostles when the risen Lord appeared by the Sea of Galilee.
What is certain is that Bartholomew left everything to follow Jesus, becoming his disciple, friend and an apostle entrusted with the continuation of his mission.