Johann Müller was a German astronomer and mathematician, also known as Regiomontanus. He studied trigonometry and completed a translation of Ptolemy's Almagest from the original Greek that had been started by his tutor, Georg von Peurbach (1423–1461). Ironically, this translation, together with some comments and observations added by Müller, helped overthrow the Ptolemaic system of the universe. Müller also observed the motion of the Moon, planets, and comets, and erected an observatory at Nürnberg, which included several modified quadrants and a few of the first weight-driven clocks.