Gerardus Mercator (5 March 1512 – 2 December 1594) was a 16th-century German-Flemish cartographer, geographer and cosmographer. He was renowned for creating the 1569 world map based on a new projection which represented sailing courses of constant bearing (rhumb lines) as straight lines—an innovation that is still employed in nautical charts.

Mercator was one of the founders of the Netherlandish school of cartography and is widely considered as the most notable representative of the school in its golden age (approximately 1570s–1670s). In his own day he was the world's most famous geographer but, in addition, he had interests in theology, philosophy, history, mathematics and geomagnetism as well as being an accomplished engraver, calligrapher and maker of globes and scientific instruments.