The armed-resistance wing — and one of the twelve disciples is introduced by the nickname.
The Zealots held that paying tribute to Rome was itself a denial of God's kingship, and acted on it. As an organised faction they are a phenomenon of the revolt of AD 66, after the gospels' events, but the outlook long predates the name. Luke lists Simon the Zealot among the twelve, which puts a man of that persuasion in the same small group as Matthew, who had collected taxes for Rome — a detail the gospels record without remark.