arch enemies

I might be mistaken, but it seems game series rarely include specific, perpetual antagonists... an enemy leader or rival who is always working against the player's character, though other enemies rise and fall.

Lex Luthor is a clear example. Even when Superman manages to catch the criminal mastermind and deliver him to prison, Luthor inevitably escapes and wreaks havoc again. The Joker is another (and my favorite) example. Though Batman faces many enemies, The Joker is a sort of polar opposite and has a way of turning up again after being defeated.

An arch enemy might work from hiding, like the Sith Lord does in the first episodes of Star Wars. Or the character might be revealed early on but is never seen in any overt action, as in LOTR with Sauron.

In games series, it seems antagonists continue on only in generalities. In Halo, it's the Covenant and the Flood. In Gears of War, it's the Locust army. There's no specific figure for the player to focus their emotions and opposition on. The opposition is national or ideological, rather than personal. I'm sure there are exceptions.

Observing that the four IPs with arch enemies listed above are some of the most popular stories in modern history, this seems to be a story and gameplay element worth considering.