Ouyang Feng
At the beginning of the story, Yang Guo encounters the insane Ouyang Feng, who likes him and accepts him as a godson. Ouyang Feng was a Kung Fu genius and had the more potential than the greats of his era but evilness and greed led him to the wrong path ultimately learning from voodoo/fake manuals concluding in him going crazy and sealing his potential forever. He is still very strong though but can never go back to his old form.