Greek Fire: What Was This Powerful Ancient Weapon?

A dragon statue emits fire as people look on during the premiere of 'Game Of Thrones' at Sydney Opera House. (Photo by Don Arnold/WireImage)

If you are a fan of the Game of Thrones, Knightfall or Dark Fall, you may have heard references made to Greek Fire. Greek Fire was a mysterious medieval weapon that helped to make the Byzantines naval forces so powerful because the substance could be easily ignited and remained burning strong even on water. Was Greek Fire a real substance? If so, what exactly was it?