Myth Monster

Myth Monster was a demon from Marvel comics (or at the very least a malevolent magical entity) - he had been active since the days of Camelot (at least 6th century) and existed to spread misinformation and prejudice towards people with disabilities: especially children, he was actually pained to see people with disabilities accepted and as such he was definitely one of the more insideous villains in Marvel as he literally grew stronger from the suffering of others (the fact that he targetted children made him especially cruel).

However like many demons Myth Monster was vulnerable to forces that contrast his own sphere of influence: namely the truth, once people reject Myth Monster's lies and gossip he loses control over them and is forced to flee - in many ways he could be considered a symbolic villain (embodying ignorance).