Madame Popovawas a contract murderer in Russia in the late 1800s until the early 1900s. She has, at the very least, three hundred known victims.
This hit-woman-for-hire specialized in executing men who were entrapping women in severely abusive relationships. She would poison her targets with arsenic for a small fee and was considered to be one of the first advocates of women’s liberation long before the cause was widely recognized.
She was apprehended after one of her clients became remorseful for ordering the death of her husband. An angry mob set out to burn Popova at the stake, but she was rescued by soldiers at the last minute. Her only attempt at a defense was her proud statement that she never murdered a woman. Madame Popova was sentenced to death and was executed by a firing squad.
source: the killer book of true crime by tom and michael philbin