"Smart" implies intelligence, ie, computer. "Robot" implies "manlike", and only in the large few years have the Japanese made a walking robot, but the hands are fingerless. The smartest computers can beat the world's best chess player, give a Math answer quicker than a human or even take care of thousands of bank accounts without error. But those are individual computers, none can replace a human for all tasks, nor would we want them to.
Since you asked for the "smartest" I'll nominate the Houdini Chess Engine which works via the Fritz Interface, marketed by the German company, Chess Base.
Chess programs like Houdini, Deep Fritz and Rybka are so strong now that even the world's best players -- people like Norwegians Carlson,Indian Anand, Russian Kramnik, and American Nakamura -- struggle against them.