A controller that can be defined by application development and used to share common data over several views. Custom controllers are defined for purposes that cannot be assigned to view controllers or component controllers, and serve as structuring element of a Web Dynpro application. Custom controllers use their context to communicate with their surroundings. They are used for manipulating data, or connecting to the back end.
Each Web Dynpro component contains exactly one component controller. This controller is automatically created during the component creation and contains a context, events, and methods. Unlike a view controller, the component controller is visible for all views in a component. This means, the controllers of different component views can access context elements or methods of the component controller. For this purpose, the component controller usage is automatically created for every view controller.
The definitions explain the difference between these 2 types of controllers.