From Boston Dynamics' website: "The Most Advanced Quadruped Robot on Earth BigDog is the alpha male of the Boston Dynamics family of robots. It is a quadruped robot that walks, runs, and climbs on rough terrain and carries heavy loads. BigDog is powered by a gasoline engine that drives a hydraulic actuation system. BigDog's legs are articulated like an animal's, and have compliant elements that absorb shock and recycle energy from one step to the next. BigDog is the size of a large dog or small mule, measuring 1 meter long, 0.7 meters tall and 75 kg weight [...]. BigDog is being developed by Boston Dynamics with the goal of creating robots that have rough-terrain mobility that can take them anywhere on Earth that people and animals can go. The program is funded by the Defense Advanced Research Project Agency (DARPA)."

Ah the possibilities...

And of course the always practical liveware version, even though slightly less reliable: