Garchomp did not originate from fanon, and the information on this page may not be entirely accurate to their canon. You may read more about this subject in the context of their canon on the following wiki(s):
Garchomp are a dual Dragon/Ground-type Pokémon species that are considered pseudo-legendary Pokémon, due to their high statistics. Their heads heavily resemble hammerhead sharks. When a Garchomp folds up its body and extends its wings, it looks like a jet plane. Referring back to a jet plane, Garchomps can move at sonic speed, thanks to its wings and the fine scales that reduce dragging. This Pokémon is the final evolution of Gible and evolve from Gabite. They were introduced in Generation IV. They are dry common inteams as they are the pseudo legendaries of their generation.
Garchomp's Mega Evolution is known as Mega Garchomp, and Garchompite is its required Mega Stone.