The MIT Cheetah—about the size and weight of a real cheetah—requires approximately 1 kW when running at 22 km/h, which translates to a cost of transport, or COT (defined as power consumption divided by weight times velocity), of 0.52. The team says this COT performance rivals that of running animals of the same size. By comparison... Boston Dynamics' BigDog has a COT of 15, which is far less efficient than their biological counterparts.
The MIT team, led by Professor Sangbae Kim, believes that electric motors are a better choice than hydraulics... His group developed its own "three phase permanent magnet synchronous motor," which reportedly doubles the torque density of the commercial motors they were using in the robot. With further improvements, the motors will help reduce the robot's COT to 0.33, which is "between the efficiency of runners and fliers in nature."
And they also incorporated biomimetic principles. A Kevlar tendon stretches from the foot to the knee, reducing the stress on the legs during stride by close to 60 percent. The bones themselves are made primarily out of a light polyurethane foam-core which is covered in a high stiffness resin, which makes them both light and strong. The researchers also gave their robot a spine, which is actuated not by individual motors but a differential system driven by the action of the legs...
I know that fans of Neal Stephenson's 1992 novel Snow Crash are thinking of the Rat Thing:
The body is Rottweiler-sized, segmented into overlapping hard plates like those of a rhinoceros. The legs are long, curled way up to deliver power, like a cheetah's. It must be the tail that makes people refer to it as a Rat Thing, because that's the only ratlike part - incredibly long and flexible.
(Read more about Stephenson's Rat Thing)
However, I'd also include the slamhound from William Gibson's 1986 novel Count Zero; I remember what an impression it made on me when I first read it when the novel first came out.
THEY sent A SLAMHOUND on Turner's trail in New Delhi, slotted it to his pheromones and the color of his hair. It caught up with him on a street called Chandni Chauk and came scrambling for his rented BMW through a forest of bare brown legs and pedicab tires. Its core was a kilogram of recrystallized hexogene and flaked TNT.