Freeze-Frame Bonus: Look closely. One of the humans in the story is Horst, Eustace's brother.
Humans Are Bastards: The ram reveals to Muriel that the reason the healing spring is all dried up is because humans came to the mountain and took over the springs. They littered it, and threw his brothers and sisters off the mountain for kicks. It's little wonder he's hostile in the present day.
Last of His Kind: The ram is the last of his brothers and sisters left who came from the healing springs' mountain, due in no small part to humans taking over his mountain.
Tragic Bigot: Through a photo album, the ram exposits to Muriel and Courage that the reason he hates humans is because they took over his home, polluted the healing spring, and left him the last goat on the mountain. In response, he drove them off and made it his mission to keep any and all humans from ever coming up the mountain again.
