Guy is just sitting in the tavern, chilling, telling everyone what to do. To Horde he tells 'you're a hero, go kill Alliance', to Alliance - 'you are hero go kill Horde'. The inspiration I believe comes from the old western movie Fistful of Dollars where a guy comes to town, stays in the tavern and plays the middle between two warring families. His goal - to destroy them both. Wrathion's goal must be something along those lines - make Horde and Alliance destroy themselves then come out on top.
He gives us some powerful items, but mere trinkets for him.
To me, it is painfully obvious no one should have any business with this guy. Both the Horde and the Alliance are stupid for doing his bidding.
Even in the case he is not evil, he is not a friend of neither Horde nor Alliance, but he has his own personal agenda.