Basil Valentine is the Anglicised version of the name Basilius Valentinus, ostensibly a 15th-century alchemist, possibly Canon of the Benedictine Priory of Saint Peter in Erfurt, Germany but more likely a pseudonym used by one or several 16th-century German authors.

According to John Maxson Stillman, who wrote on the history of chemistry, there is no evidence of such a name on the rolls in Germany or Rome and no mention of this name before 1600. His putative history, like his imaginary portrait, appears to be of later creation than the writings themselves.

During the 18th century it was suggested that the author of the works attributed to Basil Valentine was Johann Thölde, a salt manufacturer in Germany who lived roughly 1565–1624. Modern scholarship now suggests that one author was Thölde, but that others were involved. Thölde published the first five books under Valentine's name.: 138–140 

Whoever he was, Basil Valentine had considerable knowledge of chemistry. He demonstrated that ammonia could be obtained by the action of alkali on sal-ammoniac (ammonium chloride), described the production of hydrochloric acid by acidifying brine of common salt (sodium chloride), and created ethyl chloride and oil of vitriol (sulfuric acid), among other achievements. [wikipedia]