If Da Vinci's self-propelled cart was the first working design for a robotic vehicle, then the robotic knight would have been the first humanoid robot, a real 15th century C-3PO. Da Vinci was fascinated by human anatomy and spent long hours dissecting corpses in order to figure out how the human body worked. This gave him an understanding of how muscles propelled bone. He reasoned that these same principles could be applied to a machine. Unlike most of da Vinci's inventions, Leonard apparently actually built the robotic knight, though it was used primarily for entertainment at parties thrown by his wealthy patron Lodovico Sforza.
Da Vinci's robot has not survived and no one knows exactly what it was capable of doing, but apparently it could walk, sit down and even work its jaw. It was driven by a system of pulleys and gears. In 2002, robotics expert Mark Rosheim used da Vinci's notes to build a working model of da Vinci's robotic knight and some of the concepts behind it have subsequently been used by Rosheim for the design of planetary exploration robots to be used by NASA. So after half a century of space exploration, da Vinci's designs have finally made it into outer space.