William Kunnecke (1850 – after 1919), known as The Human Monster, was a German-American murderer and suspected serial killer, convicted of murdering farmhand Andrew Demler in South Dakota, and suspected of two previous killings in Idaho. Kunnecke was found guilty of Demler's murder and sentenced to life imprisonment at the South Dakota State Penitentiary, from where he escaped in 1919, never to be seen again.