Johannes Müller von Königsberg (6 June 1436 – 6 July 1476[1]), better known as Regiomontanus (/ˌriːdʒioʊmɒnˈteɪnəs/), was a mathematician, astrologer and astronomer of the German Renaissance, active in Vienna, Buda and Nuremberg.

In 1451 he continued his studies at Alma Mater Rudolfina, the university in Vienna, in the Duchy of Austria, where he became a pupil and friend of Georg von Peuerbach.

Regiomontanus also made the acquaintance of the leading Italian mathematicians of the age such as Giovanni Bianchini and Paolo dal Pozzo Toscanelli who had also been friends of Peuerbach during his prolonged stay in Italy more than twenty years earlier.

[2] Next he went to Buda, and the court of Matthias Corvinus of Hungary, for whom he built an astrolabe, and where he collated Greek manuscripts for a handsome salary.

[6] In 1471 Regiomontanus moved to the Free City of Nuremberg, in Franconia, then one of the Empire's important seats of learning, publication, commerce and art, where he worked with the humanist and merchant Bernhard Walther.

According to a rumor repeated by Gassendi in his Regiomontanus biography, he was poisoned by relatives of George of Trebizond whom he had criticized in his writing; it is however considered more likely that he died from the plague.

De triangulis omnimodis was one of the first textbooks presenting the current state of trigonometry and included lists of questions for review of individual chapters.

Knowing these ideas will open the door to all of astronomy and to certain geometric problems.In 1465, he built a portable sundial for Pope Paul II.

[12] Much of the material on spherical trigonometry in Regiomontanus' On Triangles was taken directly[dubious – discuss] from the twelfth-century work of Jabir ibn Aflah otherwise known as Geber, as noted in the sixteenth century by Gerolamo Cardano.

[13] Simon Stevin, in his book describing decimal representation of fractions (De Thiende), cites the trigonometric tables of Regiomontanus as suggestive of positional notation.