How are default engine classed included?

Hello

I have my own class for i.e my Character and it’s called APlayerCharacter. When I need to use APlayerCharacter I need to include it in my other classes as usual. However I have noticed when I want to use ACharacter on another Actor that inheirits from StaticMeshActor I do not need to include the ACharacter, but I need to include APlayerCharacter. So my question is where is ACharacter included? And could I possible change so that my APlayerCharacter gets included instead of ACharacter because I am only going to use my character in my game and not an default ACharacter?

Thanks