Great Spirit

The Great Spirit(G.S.) is the Strongest of all the spirits. and in the English Anime it was called King of Spirits

About
The great spirit is the oldest and most powerful Ghost on the planet. It is nothing more than a shapeless mass of trillions of ghosts interconnected. All lifeforms no matter how big or small end up back inside it. The power of this ghost is so immense that most normal people can not even look at it without fainting. Only one person the shaman king can even touch and control this ghost. It even has the power to change history by changing the world.

History
The great spirit is guarded by the Patch tribe for eternity. They are the ones that find a worthy shaman to wield the great spirit's power by hosting the Shaman fight every five hundred years. The great spirit past was a difficult one. Fifteen hundred years ago the shaman king created a big volcanic eruption that kill one-third of earth's population. According to the patch records Jesus himself was king using that power he created a lasting peace and created Christianity. Buddha was also a king. Buddha created a new spiritual realm called nirvana and created Buddhism.

The great spirit now is resting and awaits it's new owner. The king this time was Hao but he was eventually stopped by Yoh and his friends. The fate of the great spirit is currently unknown since the Shaman king ending was never shown.

Anime/Manga Difference
In the anime the great spirit was worried that Hao might get him. The Great spirit had the power to transfer any feelings it had to the surrounding area which it did with the Patch and the remaining shamans. Hao succeeded in gaining the Great Spirit and had the Spirit of Fire eat some of it. Asakura Hao was eventually cut in half by Asakura Yoh and killed ending the fight and dissolving the oversoul Patch Village. The Great Spirit was freed from Hao and the Destiny Star that announces the Shaman Fight comes again and the fight starts all over again.