Wrathion is neutral evil, if you know the old D&D alignments. He acts like a rogue(more like a godfather) and manipulates people, assassinate people too if they are in the way of his goal. I remember the rogue legendary quest, where rogues first did meet him, well. Breaking legs and giving out kill orders.
However he seems sane unlike his father.(who is chaotic evil, most insane and demons are)
If build up correctly he could be a great villain. A chessplayer manipulating and outsmart people. you need a sherlock to defeat him in the end.