Controllers, like constraints, handle the animation tasks in a scene. They store animation key values and procedural animation settings, and they interpolate between animation key values.
For information about how to assign an Animation Controller, see Assigning Controllers.
Some parameters, such as non-positional modifier settings, do not receive a controller until you animate them.
As soon as you change an animatable parameter like this with Auto Key on or add a key, 3ds Max assigns a Animation controller to the parameter. This assigned controller is a default type, depending on the parameter, but you can assign different controllers for different effects.
Animation controllers are organized in the following categories: