Everyone here loves Courage, but who exactly is he? He's a scared dog that does whatever he can to protect his home, Nowhere.
Where is Nowhere? Is it the place where there is nothing? No one? No hope? Hell?
Courage protects his home and makes sure no one harms Muriel. His master sits in his chair and hates everything and everyone. Whenever something evil comes to attack or rule over Nowhere, Courage fights back. He keeps Muriel safe and Eustace's home from being destroyed.
Muriel always sees a new head on Courage whenever something evil comes to warn her, giving him multiple heads.
Courage will forever stay in Nowhere (Hell) to protect his home, keep Muriel (humanity) safe from evil (Le Quack [greed], Fred [murder], Katz [hate], etc). His master, Eustace (Satan), will rule over and hate all that is Nowhere (Hell).
He is stuck in the middle of Hell and loves his home. He is Cerberus, our courageous, cowardly dog.