Gorazd the Old was a mage. He once offered Geralt 100 gold for the opportunity to carry out an examination of witcher eyes, 1000 to dissect one — not right then and there, whenever Geralt was "ready". He was one of "the Fourteen" who died on the hill at Sodden.
The Witcher
Kalkstein's eagerness to carry out tests on the witcher might be a nod to Gorazd in the novels.