Johann Joachim Becher was a German physician, alchemist, precursor of chemistry, scholar, polymath and adventurer, best known for his development of the phlogiston theory of combustion, and his advancement of Austrian cameralism.

The phlogiston theory, a superseded scientific theory, postulated the existence of a fire-like element dubbed phlogiston contained within combustible bodies and released during combustion. The name comes from the Ancient Greek φλογιστόν phlogistón, from φλόξ phlóx (flame). The idea of a phlogistic substance was first proposed in 1667 by Johann Joachim Becher and later put together more formally in 1703 by Georg Ernst Stahl. Phlogiston theory attempted to explain chemical processes such as combustion and rusting, now collectively known as oxidation. The theory was challenged by the concomitant weight increase and was abandoned before the end of the 18th century following experiments by Antoine Lavoisier in the 1770s and by other scientists. Phlogiston theory led to experiments that ultimately resulted in the identification and naming (1777) of oxygen by Joseph Priestley.