View Controller Object
A Controller Object is typically a 2D shape or 3D primitive that can drive the animation for a portion of a rig, instead of actually animating the underlying joints or character mesh directly. Controller objects can be located directly at the location of the action component to be controlled, or can be offset somewhere else for easy access. Offset controllers are common with Osipa-style facial control rigs. These objects can be splines, text, or some arbitrary shape that is useful to communicate what the controller is driving.
Over the last 20 years or so, good practice has evolved to use controller objects for character animation, as opposed to directly animating the joints or bones. Controllers add a layer of abstraction into the rig, which allows both for simplification and for animation data portability. Also, controllers can map to several different objects as determined by the rigger or technical director, as opposed to just a single element or component.