Scourge was an evil tom who wanted to take over the forest. But have you ever thought of how he turned so evil? It was because he was judged as a kit for his puny size and because he was bullied by Ruby and Socks. Scourge wanted to prove himself, but was blinded and took the wrong path.
Scourge was a good cat and could've been a great hero if he hadn't took the wrong turn. He could've joined the Clans if he wasn't attacked by Tigerstar (Tigerpaw then). But Scourge ran and met friends along the way. He didn't stay with those friends.
When Bone told Scourge about the dog in the alley, Scourge thought of it as a way to prove himself and show cats that he was strong. When the dog ran away from Scourge's shadow, he decided that everyone should respect him. That's when Scourge took the wrong path. That's what messed up his life.
What if Scourge never turned evil? Imagine him as a friendly yet strong alley cat who was generous and wise beyond his years. But his siblings' taunts rung in his mind, and Scourge wanted it to stop.
