Gemma Frisius (/ˈfrɪziəs/; born Jemme Reinerszoon; December 9, 1508 – May 25, 1555) was a Frisian physician, mathematician, cartographer, philosopher, and instrument maker. He created important globes, improved the mathematical instruments of his day and applied mathematics in new ways to surveying and navigation. Gemma's rings, an astronomical instrument, are named after him. Along with Gerardus Mercator and Abraham Ortelius, Frisius is often considered one of the founders of the Netherlandish school of cartography, and significantly helped lay the foundations for the school's golden age (approximately 1570s–1670s).