Regiomontanus, a German mathematician and astronomer whose name was Johann Müller, was born at Königsberg in Franconia, 6th June 1436. From his birthplace he called himself in the mediæval fashion Johannes de Monteregio; since 1544 Regiomontanus is the name by which he has been known. He was trained by the Austrian mathematician George Purbach (1423–61), studying under him at Vienna and elsewhere. In 1461 he accompanied Cardinal Bessarion to Italy in order to learn Greek. He sojourned in Rome, Ferrara, Padua, and Venice; returned for a time to Vienna, and was called by Matthias Corvinus to his court at Buda; but in 1471 he settled in Nuremberg, where a learned and wealthy citizen, Bernhard Walther, subsidised him so as to enable him to construct mathematical and astronomical instruments and found a famous printing-press. The two laboured together at the correction of the 'Alphonsine Tables,' and jointly published Ephemerides 1475–1506 (1473), of which Columbus and other early navigators made much use. Regiomontanus not only worked at astronomy, but restored the study of algebra in Germany, extended the science of trigonometry, and published treatises on water-works, burning-mirrors, weights and measures, &c. He was summoned to Rome by Pope Sixtus IV. to assist in reforming the calendar, was made Bishop of Ratisbon, but died at Rome, 6th July 1476.
Among his works are De Doctrina Triangulorum (1463); De Quadratura Circuli (1463); Calendarium (1473); De Reformatione Calendarium (1484); De Comte Magnitudine (1531); De Triangulis Omnimodis (1533). See Ziegler, Regiomontanus, ein geistiger Vorläufer des Columbus (1874).