Every one was perfect in the land of the gods. Tall, lithe and goodlooking, they never grew old. Supermodels of both sexes. Olympic athletes, the lot of them.
The king of the gods, Zeus and Hera, the earth goddess slept together and had a baby (one of many) called Hephaestus. But Hephaestus was no super baby. His legs were small and twisted behind his back.
His mother didn't want a deformed child so she threw him out of heaven.
Splat. Onto earth.