Diablo/Zhar, the Mad

At catacombs level 8, find Zhar, the mad sorcerer that thinks he's powerful. Talk with him and he will hand you a random spellbook. However, he will warn you to not touch the bookcase, since the wisdom contained there is only for him.

To anger him, grab the book on the bookcase and he will start attacking you. He is somewhat tough but some blows may kill him. When dead, he will drop a random item that can be unique, magic or even normal.