At the catabumbs level 5, back to town and talk with Griswold. He will tell you about some caravan with strange folks that, years ago, passed through Tristram. Stayed just a few days at the Tavern of the Rising Sun and left. The wierd thing is that he heard something about a "magic rock" at their carriage.
That caravan went to the dungeons, he don't know why, and by what he knows, they went attacked and perish. But the stuves on the carriage are still there. He will ask you to bring him that "magic rock" and, if is true that it has magial powers, maybe he can do something for you.
Back track to catacumbs level 5 and seek for that rock. It will be somewhere there. Probably guarded by a horde of demons. Get it and handle to Griswold that will make the unique item: Emperor's Ring for you (very good magical bonuses indeed).