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).