When Darth Sidious rescued Darth Vader on Mustafar, the medical droid provided two options for his body. Option 1, a more mobile body (the one seen in the movies) and Option 2. This is what Darth Vader would have looked like if his master chose the latter.
Fourth Wall Commentary
Happy 2011 everyone! At first, this started out as a flying saucer tablescrap. Then it turned into a flying saucer with arms, and so on. And then this was born. So yeah, 2010 was a great year and I can't wait to see what 2011 holds.