Fredegund
Fredegund (545 – 597 CE), the queen consort of Chilperic I – the Merovingian Frankish king of Soissons, has a reputation of being one of the most bloodthirsty and sadistic women in history. Accounts by Gregory, the Bishop of Tours (539 – 594 CE), depict her as a murderous lady who achieved power through her husband and used it to keep his kingdom in a state of war for more than forty years. She was also known as an early exponent of dirty warfare who relied heavily on poison and other covert operations
Martini Fisher 