Green’s Dictionary of Slang

promoter n.

[the fraudulent schemes he ‘promotes’; note Holyoake, Dict. (1617): ‘A promotour, which, having part of the forfeit, bringeth men into trouble’; Nares, Glossary (1822), defines promoter as ‘an informer’]

[early 17C; late 19C–1910s] a confidence trickster.