Controller objects are simply proxy objects which have their advanced hierarchy options set to control objects instead of directly participating in the tree. We don't use the term much anymore.
A good example is a proxy point that controls the rotation of 4 wheels on a car. The proxy rotation is set to “Act around child's pivot”. Therefore the proxy doesn't move itself and the wheels rotate around their own axes. You only have to modify the animation of the proxy to control the animation on all its children.
Andy le Bihan - 2005-12-27