The Controller pattern assigns the responsibility of dealing with system events to a non-UI class that represents the overall system or a use case scenario. A Controller object is a non-user interface object responsible for receiving or handling a system event.
A use case controller should be used to deal with all system events of a use case, and may be used for more than one use case (for instance, for use cases Create User andDelete User, one can have a single UserController, instead of two separate use case controllers).
It is defined as the first object beyond the UI layer that receives and coordinates ("controls") a system operation. The controller should delegate the work that needs to be done to other objects; it coordinates or controls the activity. It should not do much work itself. The GRASP Controller can be thought of as being a part of the Application/Service layer [2](assuming that the application has made an explicit distinction between the application/service layer and the domain layer) in an object-oriented system with Common layers in an information system logical architecture.