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 a 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. He knows nothing but hate, despise and greed. Whenever something evil comes to attack or rule over Nowhere, Courage fights back, keeping 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 stay forever in Hell (Nowhere) to protect his home, keeping mankind (Muriel) safe from the evils of Hell (Le Quack [greed], Naughty Fred [murder], Katz [hate], etc.). His master Satan (Eustace) will rule over and hate all that is Hell (Nowhere).
He is stuck in the middle of Hell and loves his home. He is Cerberus, our courageous cowardly dog.