Usurper

The man who deposed and killed Fergus var Emreis and cursed his son, Emhyr. He was a Nilfgaardian nobleman who proclaimed himself emperor, but a revolution restored Emhyr and his likeness, name and lineage were erased from records and history, all his portraits defaced and destroyed. He's only mentioned in the Witcher saga as the Usurper.

Finally, I can draw again, after months of creative draught and technical issues; all solved now.