He was a villain right up until the moment that he (and his OOC buddies) got caught, and then he was just another griefer, kinda-sorta abusing game mechanics to exact revenge. Don't confuse villainy with being a troll, or being chronically predisposed to betraying your own team. 
Can you please explain how I, the player of Erasmus, abused game mechanics?
Not sure what you mean by "being chronically predisposed to betraying your own team" but I'll say that Erasmus never did anything to betray Terran (excluding his distrust and attempts to discredit Hireshemont near the end, which he saw as trying to help/save Terran) until after he felt he was betrayed by them due to all the threats and protests engineered by Hireshmont; his info was used to help Terran and D'Hara, the "spy network" was a one-way street into the Senate and Strategium of Terran--rarely used and usually unknowingly by the people he got the info from, and his other "activities" of torture and murder were pretty well known and tolerated in Terran for quite a while, including by the Chief Magistrate. I don't deny the griefing (if you mean destroying granaries/renaming recruitment centers in his region when it became apparent they were gonna ban him and try to kill him) to get revenge, though, and still have (or had, now that I hear Terran is getting jacked up badly right now) plans for more against Hireshemont and his guys
BUT, I didn't see any of that as abuse, and it seemed like something the character would do out of spite and hatred.
And, Kas was ruler of Terran?!? I'm sorry I missed that, that guy always said the funnest and craziest things
