Decanite as he was making the overworld decided that there needed to be an opposite. Thus the nether was born. Instead of the luscious green gills and the breathtaking oceans and all of the wonderful creatures that inhabited the waters and lands, He created the Nether. With awful netherack and degrading soul sand. As well as no water instead destructive lava. He created creatures of hell with destructive capabilities.
He then created Dianite to rule the nether as his own as Mianite to Mianite and Ianite to The End.
As the inhabitants of the world joined Dianite and believed his ways the more powerful he became. And the stronger his realm was standing.