Alex, from Golden Sun.
Starts off as the first Mercury (Water) adept introduced. We later find out he was charged with guarding the Mercury lighthouse alongside his clan, but betrayed them to light the lighthouses instead.
During the second game, we find out that lighting the lighthouses might not be as bad as it seems. So is he a good guy after all?
Nope, he's a scheming, power hungry traitor to humanity who has no interest in saving the world, his only goal being to take the power of alchemy and the Golden Sun unto himself and become a god.
He manipulates the major villains, and the heroes at times, without you ever knowing whose side he's truly on, or what his motives are. His mysterious nature is appealing, especially when it's revealed he's a lot simpler than he appears, and that all of that organized acting and scheming was for personal gain. It makes him work well as a villain because of how his motivations are gradually unraveled and raise questions throughout two games.
The fact that he's a water user (and apparently a very powerful one at that - one of the most powerful adepts we see in the series) is really cool too. He also has a direct relationship with who would otherwise be the most inconsequential member of the group, Mia, who is from the same clan and trained under the same master and is the same sort of adept as him.
He's a well executed villain with constant hooks thrown at the player to keep them invested in his story, a strong connection to a member of the main cast, and a perfect candidate for a big bad guy.
He's underrated, in my opinion.
