The God Hand are five demons (they call themselves archangels) of immense power. Once they were all human, but fate had chosen them when they each came into contact with the red Behelit, and at a great demonic ceremony and with a huge sacrifise they were allowed to ascend and become the demon kings they are now.
Little is known about them and their goals. They can manipulate fate and have great forsight, but even they cannot see all ends.
Unlike other demons, the God Hand cannot yet take physical form on Earth without taking a host, as Slann recently appeared possessing a pile of troll entrails. One major loophole is that during an eclipse once every thousand years, a God Hand can undergo a Rebirth Ceremony and return to Earth as Femto did, possessing the child he perverted and using it to take shape under his old identity of Griffith to carry out their work personally. With this act as well as his very birth, the two worlds are merging and soon the rest of the God Hand will be able to permanently take bodies on Earth.
The God Hand do serve a mysterious higher power. The god created by man, little is known about it save that it is called the Idea of Evil.