Diablo/Gharbad, the Weak

You will find this quest before Odgen's Sign quest (at dungeons level 4), but will complete it later.

Gharbad is a Clan unique demon that will not attack you, instead, he will beg you to not kill him in trade of an magic item. Just go to catacumbs level 5 and kill some demons. Back and talk to him. He will say that he's making you an magic item, will beg again to not kill him and so.

Repeat the same procedure like two or three times, always talking with him. At some point he will turn against you and start attacking you.

Sad dumb demon. He is so weak that makes me laugh. Just kill him and see what he drops.