Phineas Black
When Phineas was eight years old he put a silencing draught in the kneazle, Athena's, food because she wouldn't stop miaowing. An hour later he found Athena cold and unmoving in the hallway. It hadn't been a silencing draught but poison in the vial. Phineas wept for a week.
From that moment on, he was very careful not to hurt people or animals. He healed the sick animals that he rescued from his little sister Belvina, he brewed a hangover potion for the old man in the Leaky Cauldron and was always ever so careful to not hurt anyone. When he turned seventeen and went on his first Muggle hunt with his father and uncles, he hid behind a tree afterwards and vomited until he couldn't vomit anymore.
But he still made sure not to hurt anyone. When his Aunt Elladora stood before the Wizengamot and declared in passionate tones why muggle hunting should not only be allowed, but encouraged, he didn't raise his wand to vote in favour. The bill failed and Aunt Elladora glared at him with venomous hatred. He raised his lit wand for the next bill - in favour of muggle rights.
When he arrived home that evening he was met with a curse and he dodged. Phineas dodged and shielded, stepping always backwards and away from the fight, never using any curses against his family even as the air grew thick with theirs. He stepped backwards outside of the wards and disapparated away. He never wanted to hurt anyone ever again.