In the Acts of the Apostles (Acts 1:13), Luke gives Simon the name “the Zealot,” which probably means that he once belonged to the group known as the “Zealots.” The title “Cananean,” used by Matthew and Mark, most likely means the same thing in Aramaic—“full of zeal”—rather than referring to a place like Cana.
Jude, the son of James (whom the liturgy and many traditions identify with the “brother of the Lord” and with the author of the New Testament letter that bears his name), is the apostle also called Thaddeus. Because of confusions with others of the same name, both Simon and Jude came to be associated with legendary stories—some perhaps containing historical elements—that actually belong to different figures.
We know nothing certain about their missionary work or the circumstances of their deaths. In the Eastern Churches, the two apostles are honored on different days: May 10 for Saint Simon, and June 19 for Saint Jude.
