Dark Cyborg, Silencer of the Living

When he was young, Star-Eyes the Hopeful was sold by his halfling parents into slavery. He tried to make the best of it, smiling and laughing through the beatings of his new master any time he made a mistake, but each one was another scar that weighed on his heart.
He was happy when the old coot finally died, but the happiness turned to sorrow when he found himself in possession of the master's son instead of being free, as the old man had promised. And so he continued working, continued enduring the beatings which were dealt by younger, stronger hands, and continued trying to smile. When all else failed, he always was able to smile...
That is, until the son took him to handle his things when he went on a trip to a nearby halfling settlement. Even though Star-Eyes hadn't been there for twenty years, the place hadn't changed one bit - even his parents were still there. The bitterness and pain melted away when he saw that they were living on scraps, barely making it, and he understood why they had done what they did. But when he tried to go to them, his master stopped him. When he asked politely, his master sneered, chopping them both down with his blade while Star-Eyes watched. It was the day he stopped smiling. It was also the last day that his master lived, for Star-Eyes quickly threw him into the fire and jumped on his corpse until even the ashes gave way under his tiny weight.
Star-Eyes was badly hurt, and the town wanted nothing to do with someone willing to murder another sentient being. So he walked into the unknown, eventually collapsing from his injuries near a gnome settlement. Even though he wasn't dead, a gnome tinker took him in and experimented on him, replacing dead or failing flesh with mechanical wonders of his own design.
When Star-Eyes awoke, the gnome explained what he had done to save him, and he was thanked with a bullet through the brain. Most still don't notice him, though soon all the world will know the name Dark Cyborg, and they will pay in blood for his suffering, be it past, present, or future. They all. Will. Pay.