Son of Claude Delisle (1644-1720), historian and geographer to the King of France, Guillaume drew his first maps at a very early age. A student of Giovanni Domenico Cassini (1625-1712), he produced his first manuscript terrestrial globe in 1699, encapsulating the most advanced geographic knowledge of his day. In 1718, Delisle became First Geographer to Louis XIV (1638-1715), King of France - a new position created especially for him, which he held until his death. In his mapmaking, Delisle not only corrected errors handed down from his predecessors, but also eliminated the imaginary lands that filled still-unexplored regions in earlier maps and globes. Delisle was one of the most important reformers in French cartography.