Serena the Excommunicated

Serena is one of a minority of heroes whose names has been struck from the official records and exists now only in informal documents and crime watch lists. Honestly, overall her deeds were not the most terrible thing ever recorded, but she did it to the wrong people and it was bad enough she deserved consequences like having her name eternally dragged through the mud.
Serena was clever. This in itself was not a bad thing, even if it did lead her to great success as a Hero. The difficulty came from the fact that she believed herself to be more intelligent than the law. She was smarter than those who attempted to catch her once things got going, but that was not the issue as much that she thought herself better than following each law. She knew better, her own choices allowed exceptions, and she was never wrong about it.
Aside from the obvious arrogance and problems with the more reasonable laws like the ones against theft and vandalism and generally harming people's property, it meant that when confronted with her own actually idiotic choices she refused to acknowledge them as anything less than brilliant.
She was pretty, according to the records from before she did what she did. Curly brown hair, nice teeth, a dashing smile. People used to like her, before they associated her with poison.
She didn't even make the poison herself. She stole it from someone who was meant to keep it safe, which was its own problem, but then she decided that she knew what it was for and she used it according to her own theories. Never mind that she didn't so much as test it. She sniffed, and then apparently she "knew." She was clever, after all.