Louis-Jacques Thenard (born May 4, 1777, La Louptière, Fr.—died June 21, 1857, Paris) was a French chemist, teacher, and author of an influential four-volume text on basic chemical theory and practice (1813–16).
A peasant’s son, Thenard endured extreme hardships to gain his scientific education. His several teaching posts were obtained through the influence of Nicolas-Louis Vauquelin, who also arranged Thenard’s succession to his own chair in chemistry at the Collège de France in 1802. He later taught at the École Polytechnique and the Sorbonne and eventually became chancellor of the University of Paris.
In 1799 he discovered Thenard’s blue, a pigment used in the colouring of porcelain. He did much notable research with his friend Joseph-Louis Gay-Lussac. His independent achievements included studies of esters (1807), the discovery of hydrogen peroxide (1818), and work in organophosphorus compounds. He became a baron (1825), a member of the Chamber of Deputies (1828–32), and a peer (1832). His native village was renamed La Louptière-Thenard in his honour (1865).