(from the http://www.bibleinfo.com/en/questions/who-were-twelve-disciples webpage)
Simon, the Zealot, one of the little-known followers called the Canaanite or Zelotes, lived in Galilee. Tradition says he was crucified.
In two places in the King James Version he is called a Canaanite (Matthew 10:4; Mark 3:18). However in the other two places he is called Simon Zelotes (Luke 6:15; Acts 1:13).
The New Testament gives us practically nothing on him personally except that it says he was a Zealot. The Zealots were fanatical Jewish Nationalists who had heroic disregard for the suffering involved and the struggle for what they regarded as the purity of their faith. The Zealots were crazed with hatred for the Romans. It was this hate for Rome that destroyed the city of Jerusalem. Josephus says the Zealots were reckless persons, zealous in good practices and extravagant and reckless in the worst kind of actions.
From this background, we see that Simon was a fanatical Nationalist, a man devoted to the Law, a man with bitter hatred for anyone who dared to compromise with Rome. Yet, Simon clearly emerged as a man of faith. He abandoned all his hatred for the faith that he showed toward his Master and the love that he was willing to share with the rest of the disciples and especially Matthew, the Roman tax collector.
Simon, the Zealot, the man who once would have killed in loyalty to Israel, became the man who saw that God will have no forced service. Tradition says he died as a martyr. His apostolic symbol is a fish lying on a Bible, which indicates he was a former fisherman who became a fisher of men through preaching.