I've not mentioned this often, but Egil from Xenoblade Chronicles 1 is one of my favourite antagonists from any media. The way his vengeance consumes him from being a kind, peaceful man to an extremist who is willing to sacrifice lives to kill the one he hates is done so well.
Zanza eradicated the majority of his own race, so in his need for vengeance against the man he wished to be his friend who betrayed him, he feels it's only right to do the same to the people of Bionis in recompense.
Despite this, Egil finds understanding in Shulk who personally experienced the same thoughts of vengeance and need to hurt others through his goal of trying to make them pay for taking away someone they loved.
Egil may have died but Egil took in his ideals and past as a reason to fight and later kill Zanza for the pain he inflicted upon all lives on both Bionis and Mechonis. Egil is handled so well and every playthrough of Xenoblade 1 hits so hard partly due to his charcter.