the Red-beard was a magician master. He chose Radnor
over the moderate Frobwit
as his apprentice
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.