When Lucifer the most beautiful angel fell from the grace of God and was banished to hell. He started to plot to get revenge on his dear old pops. But he lacked one very essential thing, an army.
God was ranked 3 in the top 10 strongest beings in the world, and also had heaven full of angels, ready to give their lives for him. But Lucifer didn't have anything, even if he could fight God one-on-one, he knew that he would be dead before he could touch the old man's beard. So he decided to become a God himself just so that he could the God. He became Lucifer Morningstar, the King of Hell and Ruler of Devils. Using his wife Lilith, he started creating devils, beings that were the very opposite of angels.
He appointed himself and his six loyal generals, that fought with him against God, and were banished together with him as The Satans, the rulers of UnderWorld. Once he appointed his generals, he used Lilith to give birth to 7 powerful devil houses, each created to serve him and his Lucifer clan only, to further his cause of revenge against God.
The 7 devil houses were:
1) House Lucifuge
2) House Nebiros
3) House Satanachia
4) House Algaliarept
5) House Fleurity
6) House Sargatanas
7) House De Vil
He created each house with a certain purpose. But he made a mistake in the purpose given to the last and most dangerous clan, he gave them the purpose of protecting the Devils as a whole, something that gave them the freedom to act without his permission and the ability to ignore his authority as the King of Devils.
Hence, 7 devil houses became 6. And the last became Shadow Clan, led by the emperor of shadows, Skygge De Vil.
But the surprising thing was that even after their supposed betrayal of their King, they were never eradicated, one could only wonder, as Lucifer was anything but merciful.