In case you have never played a game in the Diablo series and was wondering where it got it's namesake, its this guy. Al'Diabalos is his real name, but more commonly known as Diablo, Lord of Terror. In the Diablo Lore this guy is the youngest of the Prime Evils, but also the strongest and main antagonist in the Diablo games.
Diablo has had a different appearance in the Diablo series. In Diablo 1 he is depicted as a giant humanoid with red skin, claws and spikes. In Diablo 2 he changed a bit. This time he has a trail and more spikes and acts more beast like (charging on all fours). As for Diablo 3 his appearance was revealed at Blizzcon 2009 in where he is shown to be leaner, more skeletal than previously while also having 4 arms. His trademark feature that we don't know the Diablo Lore behind is the mouths he has on each of his shoulders.
Considering Diablo can take any form or shape, it is unclear whether we see is his true form. However his form in Diablo 2 may be the closest to his true form, as the player fights him in Hell. Some also say that his true form may be revealed in Diablo 3, where the destruction of the Worldstone allowed Diablo to enter Sanctuary from another dimension, where as before he had to possess a human and transform. Another explanation might be that Diablo (as mentioned in the Sin War novels) is said to take on the form which is most frightening to whoever is watching him.
Discussions about Diablo Lore and his true form can be found here and here.
The realm ruled by Diablo is that of terror, but this has a very small population as even demons cannot stand it's torment. Diablo was the last of the Prime Evils to be trapped in the Soulstones during the Dark Exile. His Soulstone was sealed in a cave system and a monastery was built on the location. Very similar to what Mephisto did, Diablo spent ages slowly corrupting the Soulstone until he could finally use some of his powers. He used these powers to possess King Leoric and Lazarus, his archbishop.
A small note, but King Leoric is resurrected in Diablo 3 from the power of the fallen star, becoming the Skeleton King and raising undead to attack Tristram.
Continuing on the Diablo Lore.... King Leoric proved too strong to fully possess, so instead Diablo went for his son, Prince Albrecht. Diablo used these minions to cause havoc in surrounding land, attracting many heroes to cleanse it. The strongest of these adventurers finally reached the goal (Diablo's Soulstone), but was so corrupted by Diablo's influence that he believed the only way to truly banish the demon was to insert the Soulstone into his own head. This, being Diablo's plan all along, gave him a body which he could to free his brothers.
The adventurer ofcourse being the player, here is the ending where you plunge the Soulstone into your forehead and become the Dark Wanderer:
Diablo was eventually killed by other adventurers, and this time they destroyed his Soulstone in the Hellforge. Whether or not this actually put a permanent and to Diablo is yet to be seen, but he is confirmed to be in Diablo 3.
Some interesting Diablo Lore:
- Diablo is content leaving the power-hogging games to his brothers while he revels in pure destruction.
- Rarely speaks
- Also known as the "artist of terror" because of his creativity
- The strongest Demon known so far
- Can control massive amounts of Fire magic