C19: from the phrase the real Simon Pure, name of a character in the play A Bold Stroke for a Wife (1717) by Susannah Centlivre (1669–1723) who is impersonated by another characterin some scenes
simon-pure in American English
(ˌsaɪmənˈpjʊr)
adjective
genuine; real; authentic
Word origin
after Simon Pure, a Quaker in Susanna Centlivre's play A Bold Stroke for a Wife (1718), who must prove his identity against an impostor's claims