Decimated and UVed.

Chopper is a reindeer that ate the Hito Hito no Mi which is a devil fruit that allows its user to transform into a human hybrid or a human at will. He came from Drum Island where he learned how to be a doctor, and is the only member of the Straw Hats who was born on the Grand Line. His dream is to one day become a doctor capable of curing any disease and wants to travel all across the world specifically in the hopes of accomplishing this dream.