Andrea Von Strucker (Viper/Madame Hydra)
She is the supreme commander of H.Y.D.R.A.. As Madame Hydra, she took control of H.Y.D.R.A.'s New York branch, and from there the rest of Hydra. Viper is a master of poisons, and is immune to almost all toxins. In fact, she uses a poisonous lipstick to give her foes a literal "Kiss of Death".