On the matter of his disfigurement, portraits apparently show no evidence of a hunched back. Of course, portraits then were frequently kinder to the sitters than they deserved, at least until Cromwell insisted he be portrayed "warts and all". However, there is no reference to such a deformity in contemporary written accounts either and they were often less than flattering. The most that can be said, apparently, is that he had one shoulder slightly higher than the other. That was enough to permit Shakespeare and others to show poor Richard as a twisted monster in order - as the earlier answer says - to soft-soap the current ruler.