The surest way to show that a hero is an undeniably awesome good guy is to show him hanging out and totally loving his dog. I mean, it's his dog. Who ever heard of a cool dude that doesn't love his dog? Think of this trope as being the physical manifestation of Pet the Dog. If a character has a dog which is around him constantly and whom he is always nice, respectful, and loving to, then that means a scene literally cannot go by in which he does not Pet the Dog. So of course he must be noble and good at heart. Contrast Right-Hand-Cat, compare Kindhearted Cat Lover.