Called Zelotes - Some Jews gave this name to themselves, according to Josephus, (War, b. iv. c. iii. s. 9, and vii. c. viii. s. 1), "because they pretended to be more than ordinarily zealous for religion, and yet practised the very worst of actions." "But this (says the judicious Bp. Pearce) Josephus says of the zealots, at the time when Vespasian was marching towards Jerusalem. They probably were men of a different character above forty years before; which was the time when Jesus chose his twelve apostles, one of whom had the surname of the Zealot." It is very probable that this name was first given to certain persons who were more zealous for the cause of pure and undefiled religion than the rest of their neighbors; but like many other sects and parties who have begun well, they transferred their zeal for the essentials of religion to nonessential things, and from these to inquisitorial cruelty and murder. See on Matthew 10:4 (note).

Matthew and Thomas,.... The first of these was a publican, and who also was called Levi; and the latter had besides the name of Didymus, and was he that was so unbelieving of Christ's resurrection:
James the son of Alphaeus; sometimes called James the less, and the brother of our Lord: and
Simon called Zelotes; or the Canaanite; See Gill on Matthew 10:4.

Simon called Zelotes - Full of zeal; otherwise called Simon the Canaanite.