Delphi's components reside in the Visual Component Library (VCL) . The following figure shows the relationship of selected classes that make up the VCL hierarchy. For a more detailed discussion of class hierarchies and the inheritance relationships among classes, see Object-oriented programming for component writers Index.
The TComponent class is the shared ancestor of every component in the component library. TComponent provides the minimal properties and events necessary for a component to work in the IDE. The various branches of the library provide other, more specialized capabilities.
When you create a component, you add to the component library by deriving a new class from one of the existing class types in the hierarchy.