Seasonal Dragons take on the characteristics of the season during which they are born. Thus, eggs that are laid in spring match the pink flowers and green buds of spring, and those that are laid in the summer grow to depict the bright green of the forest trees and the yellow of the sun. Eggs laid in autumn display the bright colors of leaves falling from trees, and those that are laid during winter take on the appearance of the icy snow.

Dragons are highly-intelligent reptilian creatures that—from a human perspective, at least—appear to live forever. Many different varieties of dragon exist, each with their own unique qualities, habitats, and behavior. Adolescence in dragons is usually marked by the growth of a hatchling’s wings, although not all breeds of dragons grow wings and some breeds have other traits that indicate the beginning of maturation. In Galsreim, dragons and humans coexist peacefully.

He is said to be the best Shadowhunter of his age, having been trained severely by his father prior to his death.  Clary describes him as having the face of an angel, or a painting of an angel, with a sharp profile and features. His good looks make him popular with girls, although he has never had a serious relationship. He is sometimes very arrogant and fractious, but is a very kind, passionate, and thoughtful person underneath, as well as having an unusual, very cynical sense of humor. He falls in love with Clary.  Jace, like Clary, has as a result of Valentine's experiments more angel blood in him than the average Shadowhunter, which gives him the ability to jump supernaturally high. Jace is stabbed in the heart and killed by Valentine but Clary, through the Angel Raziel, brings him back to life.