Rigging the pelvis
If you want your character to move like Elvis, you'd better pay attention to its pelvis. The technique we're going to see in this recipe is often called "inverted pelvis", and you'll understand why when you go through the next few paragraphs.
This approach is very useful to achieve more relaxed poses with your characters. The pelvis is usually the first bone in the spine chain and, because of the nature of the bone structure, its pivot point for transformation is not at the ideal position for the twist movement that we can do with the pelvis. That's because our actual center of gravity is closer to our belly button than it is to the base of the bone.
The next screenshot shows a balanced pose that is easier to achieve with this ...