Simon was one of the twelve apostles and is distinct from Simon Peter, the leader of the twelve. Zealots were a rebellious group within Judaism at the time of Jesus who campaigned for the political liberation of Palestine from Roman rule by force if necessary. Many of them were brutally executed by the Romans for their efforts.
Perhaps the equivalent in political terms today would be dissident republicans who see themselves as the inheritors of pursuing political change by force and by violent means.
The conversion of Simon from this Marxist mission is a sign of hope for all who try to force change by violence, even though their cause might be just. Jesus showed Simon as he continues to show us today, the way of non-violent resistance and how it achieves more, in the long term, than any victory caused by bloodshed. There are many traditions about how Simon dies, the most famous one of him being martyred by being sawn in half in Persia. This is how he is imaged in the stained glass window in St Aidan's Cathedral, Enniscorthy in a large statue of him in the Basilica of St John Lateran's, Rome.
St Jude was also one of the twelve apostles and also known as Thaddeus - the apostle who asked the Lord at the Last Supper why he showed himself only to the disciples and not to the whole world. Legend has it that he died as a missionary in Beiruit while his remains were transferred to Rome where they remain today in St Peter's Basilica. He is best known as being the patron saint of hopeless causes. Perhaps this reputation is not so much about his own powers as the power of God who makes all things new. If God could raise Jesus from the dead after his execution (the ultimate lost cause) then is anything impossible for him?