Dragons
Dragons appear in a variety of shapes and sizes. Mythologically, they are spread all over the world; sometimes seen negatively, some seen as bearers of good luck, the general consensus only leads to the fact that the dragon as a myth is so widespread that it makes one wonder if gee, maybe they aren't completely a myth.
But then again, we already knew that. Dragons are generally portrayed as being lizard-like, more often than not they have wings, and come in a wide variety of colors, shapes and sizes. They are often mysterious and misunderstood.