On the General of Gehenna's Greyhawk wiki page I saw this
According to one legend, it was the General of Gehenna who created the tanar'ri and baatezu from the "impurities" within the yugoloth race using an gem-artifact known as the Heart of Darkness. According to the story, the law and chaos inherent within the yugoloths was projected into squirming larvae of the Gray Waste. The General spoke with the larvae, imprinting dark magic into their minds before having his minions herd them into the Abyss and Baator, where they evolved into the respective races of those planes.
So anybody know where I can find lore on this cryptic artifact of old? 'Cause my Google Fu has failed me :(
it also kinda gives me Shard of Pure Evil/seed of evil vibes.