Astrogarus is a talented sorcerer who appears in the graphic novel Zdrada (English: The Betrayal), the 6th novel (1st in chrolology) in that series.
He served at the court of king Radovit II the Bold who had control over witcher schools.
In The Witcher 2: Assassins of Kings[ | ]
In The Witcher 2 there is an armor which possibly belonged to Astrogarus.