Gerard, one of the most celebrated geographers of his time, was born at Ruremonde in 1512. He applied himself with such industry to geography and mathematics, that he is said to have frequently forgotten to eat and drink. The emperor Charles V. had a particular esteem for him, and the Duke de Juliers made him his cosmographer. He composed a chronology, some geographical tables, and an atlas, having engraved and coloured the maps himself. He died in 1594. His method of laying down charts is still used, and bears the name of Mercator's charts.