Prior to becoming one of the original 12 disciples he was a tax collector. He wrote the gospel of Matthew. Because tax collectors worked for the Roman authorities they were disliked, and were renowned for wringing extra money from the people. Jesus said, when they came to be baptized, a proof of their sincerity would be not to demand more than was warranted (Lk 3:13).
See also: disciples of Jesus, Matthew (Mt).