Let me tell you a story about a man who was filled with unfathomable rage. His rage wasn't like that of a toddler who had their toy taken away, or that of a hard-working man who had to work during their break. Or even that of a victim who had been bullied for many harsh years of his life. This is rage formed from loss, pain, unfairness, and betrayal. Rage accumulated for many years while being multiplied to high doses. Untreated, boiling, raw rage.
Almost everyone sees him as a monster, and there is no doubt about it. He's a vicious monster through and through. However, his rage isn't an unleashed phenomenon. It's contained, controlled, unselfish, and only released on those he deems as monsters.
While his origins are unknown to us, we only know one thing about how he does his merciless work. Anyone who has the misfortune of coming face to face with him will always be left in a mangled state, but they're never dead.
While he's never gone after the innocent, no one can trust him because of the mark he leaves behind. The mark of Dementors, beings who live to torture those with magic and leave their bodies bloodiest and full of black dust.
And yet, for some reason, this man fights the Dementors, even though he bears their mark. Some say he's a rouge Dementor. Some say he only wields their powers, but not their goal. If you ask me, however, I see him as simply a man who carries too much with him.
Though it may be unselfish, he still carries intense rage. Intense, unyielding, unforgiving, merciless, brutal, borderline demonic rage as a weapon.
A 'Madman' through and through...