Johann Müller, also known as Johann Regiomontanus (1436-1476) was a German astronomer and mathematician. He studied trigonometry, translating Ptolemy's Almagest, from the original Greek. Ironically, his translation helped overthrow the Ptolemaic view of the universe (in which the Earth was thought to be at the center of the universe). He also did work on plane and spherical trigonometry. Muller also obsesrved the motion of the moon, planets, and comets. A 108 km diameter lunar crater, called Regiomontanus (Latitude: -28.3 degrees, Longitude: 1.0 degrees), was named for Muller.

Johannes Müller von Königsberg (June 6, 1436 – July 6, 1476), known by his Latin pseudonym Regiomontanus, was an important German mathematician, astronomer and astrologer. He was born in the Franconian village of Unfinden near Königsberg, Bavaria (not to be confused with the famous East Prussian city of Königsberg (Kaliningrad), nor with Königsberg in der Neumark (Chojna)).

Regiomontanus is an ancient lunar impact crater located in the southern highlands region to the southeast of Mare Nubium. It is joined at the chaotic northern rim by Purbach crater, and to the south-southeast is Walther crater.