John Sinclair is the name as well as the protagonist of a popular German horror detective fiction series (of the pulp fiction or penny dreadful variety). Sinclair, a Scotland Yard chief inspector, battles all kinds of undead and demonic creatures. The series appears weekly and has been running since 1973. The full title is Geisterjäger John sinclair, ghosthunter John Sinclair. While falling into the category of 'pulp fiction', the ongoing series is yet remarkable for the relatively wide range of its vocabulary and the inventiveness of its plots.

John Sinclair is written exclusively by Helmut Rellergerd under the nom-de-plume of Jason Dark. Only a few of the earliest stories have been written by other authors. Over the decades the spanish painter Vicenç Badalona Ballestar has created numerous paintings and illustrations for the bestselling series.