Guillaume Le Testu, sometimes referred to as Guillaume Le Têtu (c. 1509–12 — April 29, 1573) was a French privateer, explorer and navigator. He was one of the foremost cartographers of his time and an author of the Dieppe maps. His maps were distinguished by their sophistication and detail; they influenced generations of cartographers, navigators and explorers.Le Testu was successful as a privateer during the early years of the French Wars of Religion.