Viserys is the son of Aerys II Targaryen and his sister-wife Rhaella Targaryen. He is the younger brother of Rhaegar Targaryen and the second heir of the Mad King. During Robert's Rebellion, his older brother was ultimately slain at the Battle of the Trident, so Aerys decided to send Viserys and his pregnant mother to the fortified island of Dragonstone for their safety.

Following the fall of his father, Viserys had to leave Westeros at the age of five. He lost his mother who died giving birth to his younger sister, Daenerys. He therefore considered it as an object belonging to him as well as a means of accessing the throne which is rightfully his, claiming that Robert Baratheon was only a usurper and that he is the only true king of the Seven Kingdoms.

He lived a very large part of his life in exile in the Free Cities, ruminating on his resentment towards Robert Baratheon and cultivating his paranoia of the usurper's henchmen on his trail. Viserys and his sister could only count on the few people who sheltered the last Targaryens, certainly thinking that such a famous name could be useful to them.

Illyrio Mopatis, great merchant of Pentos, granted asylum for more than a full year to Viserys and his sister. The two Targaryens thus lacked nothing during this period.