Duriel is one of the Lesser Evils. He has what has been referred to as a “twin”. The lore that is about Andariel indicates that they are not related to each other. They aren’t really siblings. The reason those two Lesser Evils are considered to be “twins” is because the actions of one of them compliments and assists what the other does (in a sick, twisted, way).
Duriel is the Lord of Pain. In the Book of Cain, Duriel is described as “brother to Andariel”. However, Andariel is described as Duriel’s “so called twin”. Their relationship gets a bit more confusing if you consider the information found about Duriel in Diablo III.
There is a journal that players can find in Diablo III that is called “Duriel, The Lord of Pain”. It is narrated by Deckard Cain.
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 – where he was slain by heroes. – Deckard Cain
So, are Duriel and Andarial actually siblings? Or, do they just function as though they are twins? There seems to be some confusion about exactly what their relationship is. Blizzard needs to make some kind of clarification so that the information about one “twin” matches the information about the other one.
Duriel is known by two different names. He is the Lord of Pain. He’s also the Maggot King. The reason for that title is obvious. Half his body resembles a gigantic maggot.
One could say that the Lord of Pain title describes his profession (and also his main interest). Duriel is known for loving torture and for enjoying the infliction of physical pain. Unlike his “twin”, Andariel, Duriel doesn’t actually care what the pain means to the recipient. He has absolutely zero interest in his victim’s state of mind, emotional response, or anything like that.
This the main difference between Duriel and Andariel. She’s mainly focused on the emotional anguish she can inflict upon her victims. Andariel thrives on causing people emotional pain in ways that affect their relationships with others. She needs to know what the anguish means to her victims. Without that knowledge, things just aren’t as interesting for her.
What Duriel is after is the screams of his victims. He doesn’t need to know anything about the victims in order to get the response he is looking for. The Book of Cain describes this as: “He appears to love the music of the screams: the disharmony of agony at a sensual level. He thinks of himself as a maestro of pain. He is interested not in mental anguish but in physical torment.”
Duriel often receives victims from Andariel. She wears down a person’s mental state until the person believes that they are worthless and deserving of the kind of physical torture that Duriel will not hesitate to inflict on them. These victims willingly choose to give themselves over to Duriel. The reverse doesn’t happen. No one leaves Duriel’s realm. He doesn’t reciprocate by sending victims to Andariel.
What does Duriel do when he runs out of victims? He actually starts torturing himself. The Book of Cain notes that Duriel will inflict excruciating pain upon himself until he is sated. He doesn’t have any specific reason to do this. It’s not like he was bored, or feeling bad about torturing people. He simply doesn’t need a reason to inflict pain on someone – even if that someone is himself. He is known to capture and torture other demons, too.
Duriel’s realm in the Burning Hells is called the Realm of Pain (as you may have guessed). It looks like a giant torture chamber. One would assume it would include everything that has been depicted in horror movies. It is set up so that Duriel can torture thousands of captives at the same time. No one enters the Realm of Pain willingly. The other demons in the Burning Hells won’t go there, not even Andariel.
Duriel doesn’t make an appearance in Diablo III. At least, not through the Reaper of Souls expansion. However, he did appear in Diablo II. He was the final boss in Act II of Diablo II.
It appears that Duriel was involved in the Dark Exile. He got summoned by Diablo and Baal for the purpose of guarding over Tyrael, who was imprisoned in Tal Rasha’s Tomb. Why would Duriel help? It is likely because he wanted to be seen favorably by Diablo and Baal (who were both Prime Evils, and likely to retake the Burning Hells). Unfortunately for Duriel, he ended up slain by the Heroes who rescued Tyrael.