Cyborgs come under the category of medical and rehabilitation robotics, as most— but not all— additions or modifications of humans with technology is due to injury or disease. Edgar Allan Poe is credited with the first story about cyborgs, his 1839 story The Man Who Was Used Up. The goal is to create functional prostheses, not cosmetically attractive ones. Generally, people who have lost a limb prefer something that is comfortable and restores as much functionality as possible to a prosthesis that looks like the missing limb, though both function and form would be best.  The biggest challenges are coordination (current prostheses move either through Bowden cables which transfer movements of other muscles or EMG signals, but brain-machines interfaces are under research), functionality (providing the equivalent range of motion, having lightweight power sources, and having embedded intelligence to automatically control actions such as stiffening a knee during a stance but relaxing it during a swing), sensing (both new sensors and how they provide feedback to a person), and safety (making sure the limb can’t move in a bad way). In real-life, no one is questioning that cyborgs are human, people with prostheses are running into legal problems. Check out the Cybathlon for an inspiring look at the state of science for real-world cyborgs.