Locusta
Locusta (or Lucusta) was notorious in Ancient Rome for her skill in concocting poisons. Along with Locusta, Canidia and Martina made the up the infamous trio of female poisoners in Roman times.
She was born in the ancient province of Gaul. Her early history remains a mostly a mystery. According to ancient historians, in AD 54 Locusta was hired by Agrippina the Younger to supply a poisoned dish of mushrooms for the murder of Emperor Claudius. Once the drug was made, the task of administering it was given to Claudius's food-taster Halotus. In 55, she was convicted of poisoning another victim, but Nero rescued her from execution and in return called upon her to supply poison to murder Britannicus.
February 14, 55 the first attempt at poisoning Britannicus proved futile, as the concoction was too weak to kill him. Angry and impatient at this failure on Locusta's behalf, Nero beat her with his own hands and bid her to make a more deadly poison to finish the task. Nero rewarded her with a vast estate and even sent pupils to her. When Nero fled Rome, he acquired poison from Locusta for his own use, but ultimately died by other means. After Nero's suicide, Locusta was condemned to die by the emperor Galba during his brief reign, which ended 15 January AD 69. She was executed along with many other of Nero's "favorites" such as Helius, Patrobius, and Narcissus. They were accompanied by other individuals that had come to rise as scum of the city during Nero's reign, led throughout the city in chains before they were finally executed.