King Viserys III Targaryen was the younger brother of the late Rhaegar Targaryen, the older brother of Daenerys Targaryen, and the paternal uncle of Jon Snow. Viserys and Daenerys were the remnants of the exiled House Targaryenfollowing Robert's Rebellion against their father Aerys II Targaryen, the Mad King.
(source GOT wiki)