Today's feast celebrates two of the Apostles, Simon the Zealot (icon at the left left), and St Jude (best known as patron of hopeless causes, pictured below). Their feast day is the same because they formed an evangelizing team. After evangelizing in Egypt, Simon joined Jude in Persia and they were martyred together in Armenia.
The Catholic Encyclopedia notes that "the name of Simon occurs in all the passages of the Gospel and Acts, in which a list of the Apostles is given. To distinguish him from St. Peter he is called (Matthew 10:4; Mark 3:18) Kananaios, or Kananites, and Zelotes (Luke 6:15; Acts 1:13). Both surnames have the same signification and are a translation of the Hebrew qana (the Zealous). The name does not signify that he belonged to the party of Zealots, but that he had zeal for the Jewish law, which he practised before his call. Jerome and others wrongly assumed that Kana was his native place; were this so, he should have been called Kanaios."
St Jude (aka Thaddeus) was a son of Mary Clopas, a sister of the Virgin Mary.
The two saints were martyred around 65 AD in Beirut, and their acts and martyrdom were recorded in an Acts of Simon and Jude that was among the collection of passions and legends translated into Latin. Sometime after his death, Saint Jude's body was brought and placed in a crypt in St. Peter's Basilica.