Johann Friedrich Schweitzer (Joannes Fridericus Helvetius, in Latin, John Frederick Helvetius, in English) (1625-1709) was a Dutch physician and alchemical writer, of German extraction. He is known for his book Vitulus Aureus (The Golden Calf, Which the World Adores, and Desires), published in 1667. Another book is Ichts aus Nichts, für alle Begierigen der Natur from 1655. He is notorious for the story that he actually carried out transmutation of lead into gold. He is also said to have been physician to the Prince of Orange of the time. His birthplace is given as Köthen, Anhalt. He is said to have known Baruch Spinoza. He was an ancestor of the philosopher Claude-Adrien Helvétius.