Vaul

A possible interpretation of Vaul before the great fuckening known as the Fall. Note his majestic beard.

Wait a moment...SHIT THIS IS NOT A HUNDRED! - Vaul realizing he fucked up the mail order for Khaine

Vaul, the Maker is the Eldar and High Elf god of smithing. He sucks at it, though, seeing as he failed to make a hundred swords in one year despite being a god.

40k Version

His name seems to be attached to other Eldar terms related to forging and production; for example, Mars (and possibly other Forge Worlds as well) is called "the Vaul-moon" by the Eldar. He's also a copy-pasted version of the real world Greek god Hephaestus/Roman god Vulcan with the serial numbers filed off.

Vaul was a pretty nice guy; not only did he forge the spirit stones that allowed Isha and Kurnous to speak with the Eldar after being forcibly separated from them by Asuryan (and later allowed the Eldar to protect their souls from Slaanesh), he spoke up for them when they were imprisoned and tortured by Khaine for doing so. When Khaine demanded one hundred mighty blades in exchange for the two gods' freedom, Vaul agreed right away. When Khaine got angry and started the War in Heaven because he only got ninety-nine blades by the time the deadline was up, Vaul forged the last one, made it better than the rest, and fought the Eldar God of War.

Unfortunately, like all nice things in the Warhammer 40,000 universe, Vaul was just too good to stick around; he was ultimately defeated by Khaine, who crippled him and chained him to his anvil for his trouble. With Vaul's punishment in place, Asuryan came in and declared the matter settled.

Like the majority of the Eldar pantheon, Vaul met his end when he got eaten by Slaanesh during the Fall of the Eldar. That said, some of his creations survive to the 41st Millennium; the spirit stones are the most numerous of these, while the "Talismans of Vaul," otherwise known as the Blackstone Fortresses, are the most powerful.

Warhammer Fantasy

Elf Hephaestus. A total badass who challenged Khaine to single combat a long time ago on behalf of Lileath and Kurnous (not the War in Heaven of 40k though). During the fight he was crippled and his eyes were ripped out, and Khaine chose to spare him and thus make him his servant. Ever since then, his blessing go almost exclusively to weapons and armor of war. He doesn't challenge Khaine again or take his own life because the mortal High Elves need his badassry and gifts to continue surviving and to eventually wipe out the Dark Elves. When forging the Widowmaker for the first time, he asked Draugnir, the first dragon, to provide the heat to make it. But the sword was evil from day one, and it sucked his life away. When the sword was cast into the mortal world, it bound the destinies of dragons and mortal elves together until one race or the other is wiped out.

In the third book of The End Times, Khaine, it was revealed that Lord Daith of Torgovann was the reincarnation of Vaul, as people had long been suspecting. He participated in the battle of Whithelan which the Wood Elves joined their High Elves brethren under the command of Alarielle (then merged with Ariel) against Tyrion's force, who was then under the influence of Widowmaker. Daith was killed by an enemy whom he had thought earlier to be death, but not before revealed to Araloth his identity.

Mythology

The war between Vaul and Khaine is at least mildly reminiscent of the rivalry between Greek gods Hephaestus (god of smithing and technology, among other things, and a cripple) and Ares (god of war). The story goes that Hephaestus' wife Aphrodite (goddess of love -- and not always the nice kind of love, cf. Slaanesh) cheated on him with Ares, because Hephaestus had a bad leg and Ares was much better-looking, which led Hephaestus to put an unbreakable, invisible net in his bed that trapped the two the next time they met; he then showed them off to the other gods, still trapped in their "embrace." Aphrodite didn't seem to have a problem with being the center of attention, but Ares was suitably embarrassed. Obviously, the situation was reversed in the grim, dark future (Also unlike Khaine, Ares isn't the god of victory, Nike is).

The Gods of the Eldar
Asuryan - Cegorach - Isha - Kurnous - Khaine - Lileath - Morai-Heg - Vaul - Ynnead