Orsino in Dragon Age 2.
Say what you will about DA2, but the fact is, having the leader of the mages turn himself into a fucking Harvester because he couldn't handle the stress of winning the fight against Meredith because Meredith is so stupid that her strategy amounts to "send a small group of Templars into fight at a time, watch the mages curbstomp them, repeat process", only to then proceed, now that he's a fucking Harvester, to kill the mages instead of the templars, is a really stupid fucking thing and made me hate him more than anyone else in the story.
All this after having spent the entire game apparently being the only mage in Kirkwall aside from Bethany/Hawke to champion not complete Mage freedom (which is stupid) but to champion compromise.
Goddamnit Orsino, you were the only one I liked aside from the Arishok, and at least I could respect the Arishok for what he did.