Locusta

Locusta is the name of a woman thought to be the first documented serial killer. She was a professional poisoner in Rome sometime during the 1st Century A.D.; she also poisoned others in her spare time. In A.D. 54, she was hired by Agrippina the Younger to kill the Emperor Claudius, which she accomplished with a poisoned dish of mushrooms. In 55, she was convicted of poisoning another victim. When Nero learned of this he sent a tribune of the Praetorian Guard to rescue her from execution. In return for this she was ordered to poison Britannicus. She succeeded on her second try, Nero rewarding her with immunity from execution while he lived. Seven months after Nero's suicide, Locusta was condemned to die by Galba on January 69.

The Doctor, Barbara Wright, Ian Chesterton, and Vicki encountered her in the year 64.