Thorman the Red-beard was a magician master. He chose Radnor over the moderate Frobwit as his apprentice
Thorman and Radnor
Also, he was the grandfather of Lia. When his daughter died, he started to weaken until his death.
Radnor knew that Thorman had in his possession the Amulet of Egreth and caused his death. Before dying, Thorman threw the amulet out of his tower, blessing it so as it finds his granddaughter.
After Frobwit trapped Radnor, Thorman's spirit appeared to Lia and lifted the curse of Egreth Castle, revealing to her that her friend is Dirinthrax, heir of Ducanthrax.