For the Great Evil, see Duriel.
Duriel, the Lord of Pain is a tome found in Act II of Diablo III.
It is found in one of Cain's Lost Satchels. Reading it adds to the Judge of Character achievement.
It reads as follows:
Duriel is the twin of Andariel. I believe that they conspired together to assist Diablo in releasing Mephisto and Baal, though they had both supported the Lesser Evils in the past. The Lord of Pain was found guarding Baal's prison — the tomb of Tal Rasha — when he was slain by heroes. — Deckard Cain