Achilles Pirmin Gasser^[1] (3 November 1505 – 4 December 1577)^[2] was a German physician and astrologer. He is now known as a well-connected humanistic scholar, and supporter of both Copernicus and Rheticus.

Born in Lindau, he studied mathematics, history, and philosophy, as well as astronomy.^[3] He was a student in Sélestat under Johannes Sapidus [it];^[4] he also attended universities in Wittenberg, Vienna, Montpellier, and Avignon.^[5]

In 1528, German cartographer Sebastian Münster appealed to scientists across the Holy Roman Empire^[6] to assist him with his description of Germany. Gassar accepted this and was later recognized by Münster as a close collaborator for his cartography of the country.^[7]

Rheticus lost his physician father Georg Iserin in 1528 when he was executed on sorcery charges. Gasser later took over the practice in Feldkirch, in 1538; he taught Rheticus some astrology, and helped his education, in particular by writing to the University of Wittenberg on his behalf.^[5][8][9]

When Rheticus printed his Narratio prima—the first published account of the Copernican heliocentric system—in 1540 (Danzig), he sent Gasser a copy. Gasser then undertook a second edition (1541, Basel) with his own introduction^[10] in the form of a letter from Gasser to Georg Vogelin of Konstanz.^[5] The second edition (1566, Basel) of De revolutionibus orbium coelestium contained the Narratio Prima with this introduction by Gasser.^[11]

He prepared the first edition (Augsburg, 1558) of the Epistola de magnete of Pierre de Maricourt.^[3][12]

Other works include:

• Historiarum et Chronicorum totius mundi epitome (1532)
• Prognosticon (1544) dedicated to Thomas Venatorius [de]^[13]
• Edition of the Evangelienbuch of Otfried of Weissenburg. His edition did not appear until 1571, under the name of Matthias Flacius who had taken over.^[14]
• Observations on comets^[15]

Gasser belonged with Flacius to the humanist circle around Kaspar von Niedbruck [de], concerned with the recovery of monastic manuscripts. Others in the group were John Bale, Conrad Gesner, Joris Cassander, Johannes Matalius Metellus, and Cornelius Wauters.^[16]