Philipp Melanchthon
Regiomontanus wrote under the Latinized name of "Ioannes de Monteregio" (or "Monte Regio"; "Regio Monte"); the adjectival "Regiomontanus" was first used by Philipp Melanchthon in 1534. He is named after Königsberg in Lower Franconia, not the larger Königsberg (modern Kaliningrad) in Prussia.