Maker

The Maker was the being that created the Fal'Cie and humans. When the maker was on Pulse, it was a happy time for both species. However, at one point the maker left Pulse, and that is how the events leading up to Final Fantasy XIII begins.

The main cast in the game don't know about the maker until late in chapter 10. When they encounter Cid Raines in the Fifth Ark, Raines explaines to them how the Fal'Cie want to destroy Cocoon (Final Fantasy XIII) so they can get the maker to return to pulse. The main cast are being used as tools to destroy cocoon, since the cocoon Fal'Cies cant destroy it themselves.