The Noble Monster is a character archetype, a set of common motifs and forms that you can use to label a thing. The Noble Monster is a trope, one I’m not sure that merits a trope page of its own.
Noble Monsters are characters who know that there is something wrong with them. Maybe it’s imposed by their society, maybe it’s something they’ve learned. Perhaps the Noble Monster is psychological, owning a worldview that they see is harmful and dangerous. Perhaps the Noble Monster is much more obvious, with a physical presence and deformity that makes them dangerous.
The Noble Monster is not powerless. This is important. The Noble Monster could probably exist as they are, as the monster. They do not fear the society as a mortal threat. They could take to the shadows, be the corruption, be the scar, and live quite happily, if they were willing to do that. Their monstrous nature does not oppose them, or if it does, it is the lesser threat. A Noble Monster’s tension comes from within, where they see the surroundings, the setting they are in, and do not want to harm it. They do not want to be outside it, but know they must – because they recognise the damage they cause to it. They use rules, orders, structures, to chain what it is inside themselves. Make the rules, follow the rules, and keep people safe.
This is not the same thing as those characters who look around themselves, and at themselves, and think they are monsters, but are not. The Noble Monster may dislike their own inhumanity, but they do not imagine it. There are traits that make them human, and there are traits that make them inhuman – they are both, and neither.
I can’t find a TVTropes page for this character archetype. It’s not the reluctant monster, who does not even realise they are a monster in the story. They are not the Secretly Beautiful. What it is that makes the monster a monster is still monstrous. They seek to grapple with their worst self, and direct their ugliness in the places and ways it can, at least, do some good.
It’s hard to explain this simply.