Along with his brothers Drogon and Rhaegal, Viserion was raised since birth by Daenerys Targaryen, however, after being fatally wounded, and then resurrected, Viserion has now fallen under the command of his new master, the Night King. Under the Night King, Viserion would blast away the Wall in Eastside with his now blue flame, allowing the Army of the Dead to enter the Seven Kingdoms