Cryorion

Legend tells of a fearsome creature living high up in the air.
It loves the smell of carnage and destruction, that is the time when it descends from high above, bringing with it its foul air and toxic effluvia. For that reason it is very well known as the harbinger of war, bringing death to whole cities and letting plants wither and die wherever it was.

A small child once found an egg on a battlefield. The child lost his whole family and home in the war that plagued this lands and decided to take care of the egg to find a new purpose in life.
As the creature hatched and grew up, it also happened to corrupt the child more and more.
By the time the child turned into an adult, the creature did grew into a magnificent large and terrifying beast. It took control over the man who did care for it his whole life and used him as a puppet to wage wars, causing chaos wherever they went.