The Usurper was the unnamed Emperor of Nilfgaard who came to power by overthrowning the legitimate ruler, Fergus var Emreis . He ruled between 1233-1257. After assuming the throne he granted the nationwide amnesty, excluding the political prisoners . He continued the conquests in the north, taking over at least the Kingdom of Maecht .
When Emhyr was only 13 years old, an unnamed nobleman led a successful revolt against the Emperor and usurped the throne of Nilfgaard. After the coup, he tortured Fergus in an attempt to force him to acknowledge the usurper's rights to the throne. Fergus resisted and was ultimately killed. Fergus' son Emhyr was cursed by Braatens into some humanoid hedgehog form (Emhyr actually means hedgehog in the Nilfgaardian Dialect) and banished from the capital of the Empire.
He was overthrowned and executed by Emhyr var Emreis' supporters in the late 50s of 13th century.
- His name is never mentioned in the Saga or games. Curiously, in Wiedźmin: Gra Wyobraźni he is referred to as "Torres" - it is not known if it's authors' mistake whether he had indeed carried a name of one of the former Nilfgaardian emperors.