The chief city administrator on Argelius II, whose body is the host for the murderous entity Redjac in Wolf in the Fold.
Hengist is an administrator from Rigel IV who serves under Prefect Jaris in the city on Argelius II. In Wolf in the Fold, he leads the investigation when a woman is stabbed to death and Scott is found holding the knife, and he presses hard for Scott's guilt as more women are killed.
Hengist is in fact the current body of Redjac, a non-corporeal entity that feeds on fear and has killed women on many worlds, including as Jack the Ripper on Earth. When Kirk exposes him, Redjac tries to take over the Enterprise computer and is beamed into space. Hengist was played by John Fiedler.