Why do Matthew and Mark list Thaddeus in the names of apostles, but Luke mentions another Judas?
The apostle Thaddeus mentioned in the Gospels of Matthew (10:3) and Mark (3:18) is one and the same as the first Judas mentioned in Luke (6:16). It is likely that this apostle had a second name that was often used to avoid confusion with Judas Iscariot. A Catholic Commentary on Holy Scripture explains:
Doubtless like others of his time he enjoyed several names, and it is natural that the early Christians should have avoided the name he shared with the traitor (948).