Here is one of the most interested bipedal wheeled robots. The Direct Drive Innovation D1 can attach to another one to become a robot dog. It has a range of 25km on empty load and runs for 5 hours in dual wheel-leg mode. This robot can overcome challenging terrains and even carry in a human in quadruped mode.
As this video shows, this robot can go down steep hills. It can also balance on two limbs. You can find out more here.