"Do you really wish to know?"
Spoilers from the books and/or adaptations to follow!
Erhan was a captain within the royal guard of malliq Nibras of Ofir and later the malliq's personal crown assassin.
In 1273, after Geralt of Rivia and Dandelion were teleported to Ofir, Erhan and the royal guard arrested them and brought them before Nibras, the King of Ofir.
Later, after Maraal was killed by Geralt, he took the rank of crown assassin.