An administrator on the planet Argelius, Hengist was in fact a non-corporeal entity which fed on the emotion of fear. He would terrorise and then kill women to produce this fear. Over his long life Hengist had been responsible for many murders, including those committed by the killed nicknamed Jack the Ripper on Earth. He could not be killed but Kirk beamed him into space, using the transporter to scatter his essence as widely as possible and so effectively ending his existence as a conscious entity. [1] 