An archenemy (or arch-enemy) is the main enemy of someone. In fiction, it is a character who is the hero's (or protagonist's) most prominent and biggest enemy.
The word archenemy or arch-enemy originated around the mid-16th century, from the words arch- (from Greek ἄρχω archo meaning 'to lead') and enemy.
An archenemy may also be referred to as an archrival, archfoe, archvillain, or archnemesis. However, an archenemy may also be distinguished from a nemesis, with the latter being an enemy whom the hero cannot defeat (or who defeats the hero), even while not being a longstanding or consistent enemy to the hero.