The second in command of the Perinany Legion and a member of its Fist of Humanity, Gustav Mageriff was a fearsome and charismatic leader. He fought bravely and without hesitation in the beginning of the Great War, when the Perinany Legion sought to restore the Council of Six and topple Javali's dictatorship.
Over time, however, the cause of the Perinany came to look increasingly hopeless. A pagan king took the throne of Lordaeron while Stromgarde lost its war against the Hesperian Alliance. Mageriff also came to question the wisdom of the Perinany Legion's insurrection against Dalaran. It was Dalaran that the Legion had always sworn to defend, and it was Dalaran whom the Legion was fighting. Indeed, Javali had been given his dictatorial powers by a popular mandate.
Eventually, Mageriff's plan came to naught, as loyalists fought and defeated him in Venege.
He was used as part of the deception that trapped the Western Legion in Venege amidst the detonation of many powder bombs. Mageriff tried to break free and kill his captors, but was struck down from behind by Niccolo Marius, who was desperate to bargain for his life.