In the beginning, there were the titans. Greek muggles believed these to be the original occupants. They were huge, butbuilt like humans. Their leader, Kronos, discovered a prophecy featuring his future children. They would be his demise. So the titan monarch took matters into his own hands. When his three sons were born, he swallowed them whole. Unbeknownst to Kronos, the third son he swallowed was not a child, but a rock. His wife had decieved him to save her child. When the third child grew, he took action. Using an enchanted scythe, he cut Kronos into peices. Because the children were immortal, they emerged unharmed and grown. 

          Togethor, Zues, Pluto, and Posieden threw their father into the deepest pit of Tarturus. They then divided their power. Posiedon was to get the seas, Pluto assigned the underworld, amd Zues the skies. Zues was also made the king. Pluto was not happy with this arrangement, leading to years of bickering.