She’s the most successful serial killer whose name you’ve never heard. Giulia Tofana killed hundreds of men in 17th-century Italy when she turned her makeup business into a poison factory, selling a deadly concoction called Aqua Tofana. Her crimes place her among the most deadly female serial killers in history, alongside the Russian noblewoman who killed over 100 people and the Hungarian Blood Countess who may have killed 650 people.