For a robot, DARPA cheetah robot is really fast. It can run 28.3 mph on a treadmill. Not sure if it will be able to maintain this feat on normal ground. Check it out.
According to the source, this robot Cheetah can run faster than Usain Bolt.
In the process, Cheetah also surpassed another very fast mover: Usain Bolt. According to the International Association of Athletics Federations, Bolt set the world speed record for a human in 2009 when he reached a peak speed of 27.78 mph for a 20-meter split during the 100-meter sprint. Cheetah was recently clocked at 28.3 mph for a 20-meter split.
Of course, not a very good comparison but it is already amazing to see this robot moving its legs so fast on the treadmill. Check out the video.