Gorthor bears the Mark of the Gods. He is blessed by all four of the great powers of Chaos, and such is the favour bestowed on him that he may re-roll failed Break tests as well as Psychology tests. He counts as having the Mark of all four Chaos gods for the purposes of army composition (ie, you can include units with any Marks, any Daemonic units, etc.). If he is on foot, any unit he joins may re-roll Psychology and Break tests as well.