It's not clear when or where stories of dragons first emerged, but the huge, flying serpents were described by the ancient Greeks and Sumerians. For much of history dragons were thought of as being like any other exotic animal: sometimes useful and protective, other times harmful and dangerous. That changed when Christianity spread across the world; dragons took on a decidedly sinister interpretation and came to represent Satan. In medieval times, most people who heard anything about dragons knew them from the Bible, and it's likely that most Christians at the time believed in the literal existence of dragons