Hagatha the Dog Witch
Hagatha, upon arriving in Chicago, had developed an allergy to cats. She tried Zyrtec, Claritin and Allegra, and all the potions and spells in her Witch Craft: Curses & Remedies book. Nothing helped. Her eyes watered, which made her face melt a little. Her nose ran constantly, and witch snot is essentially acid so she kept burning through her handkerchiefs and shirt sleeves. The only solution was to put her beloved cat, Gomez, whom she had had since she conjured him to life two centuries ago, up for adoption.
How do you want to be defined? By one action? By some opinion that could evolve? By a mistake, regrettable only with hindsight? Or by the sum of your parts? Okay, do that for other people. Start the trend.