Mysterious ancestor figure or deity revered or respected by many vampires, the first vampire, imprisoned in a demiplane
As documented in the forbidden book of the Sopedalia, Cain was the first elf ever to murder another elf, back in the Golden Age before the coming of other races to Alair. Cursed by the elven god Anfadil, he twisted the effects of the curse to suit his own ends, now horribly distorted, becoming the first vampire in the process. Believed dead, he operated under cover, bestowing the Blood Gift on more and more sentient creatures. The elves, mightier then than in later days, proved too resistant for his purposes, perhaps because their lifespans made the "eternal" life of the vampire less appealing, but with the arrival of humans Cain was furnished with all the raw material he needed, and his power grew rapidly.
The oldest of the High Clans were created personally by Cain to organize his forces, though some rebelled and abandoned his cause to pursue their own goals.
Finally, the existence of the subculture of the vampires became known to the elves, and five of their greatest heroes, led by Galoriand and Elverandil, challenged Cain in his lair. Though they defeated him, they were unable to put an end to him, and were forced instead to imprison him on the demiplane Arnora, pinched off and sealed against any conceivable intrusion.
An attempt to rescue Cain by using one of the two Primal Weapons to breach Arnora, masterminded by Cullinan, was foiled by the destruction of the Vintares Gate and the sequestering of Zero-One in the Hallows.