Savage

He was raised as a loner. His mother sent him away at a pretty young age, as soon as he was able to fend for himself. He traveled a lot, meeting other cats and learning about their way of life, but always eventually leaving them behind. When he was about a year old, he wandered into clan territory and ran into Mousepaw. He was absolutely captivated by her and the two kept meeting in secret for a while. They fell in love and eventually wanted to become mates, but Mouseeyes informed him that it was forbidden to have a mate outside her clan. So he tried to join Stoneclan. The clan cats weren't very welcoming, and he spent years trying to prove his worth. The most he ever got was finally being given a warrior name, Shadowflight.
Eventually Mouseeyes did indeed get pregnant, and the clan only treated them even more poorly, horrified at the idea of a loner's kits in their nursery. So Shadowflight began to make plans to run away with Mouseeyes and the kits as soon as they were born and were strong enough to leave. But Mouseeyes died giving birth. He stayed just long enough to see the mistreatment of his kits before he left, vowing to make the clan pay for how they treat outsiders. How they treat savages. Yeah so anyway he formed the savages inspired by the clans, and his need for vengeance.