According to an article by David Dobbs in NG (Jan 2013):
In the winter of 1769, the British explorer Captain James Cook, early into his first voyage across the Pacific, received from a Polynesian priest named Tupaia an astonishing gift–a map, the first that any European had ever encountered showing all the major islands of the South Pacific. Some accounts say Tupaia sketched the map on paper; others that he described it in words. What’s certain is that this map instantly gave Cook a far more accurate picture of the South Pacific than any other European possessed. It showed every major island group in an area some 3,000 miles across, from the Marquesas west to Fiji. It matched what Cook had already seen, and showed much he hadn’t.
Cook had granted Tupaia a berth on the Endeavor in Tahiti. Soon after that, the Polynesian wowed the crew by navigating to an island unknown to Cook, some 300 miles south, with ever consulting compass, chart, clock, or sextant. In the weeks that followed, as he helped guide the Endeavor from one archipelago to another, Tupaia amazed the sailors by pointing on request, an any time, day or night, cloudy or clear, precisely toward Tahiti.
Cook, uniquely among European explorers, understood what Tupaia’s feats meant. The islanders scattered across the South Pacific were one people, who long ago, probably before Britian was Britain, had explored, settled, and mapped this vast ocean without any of the navigational tools that Cook found essential–and had carried the map solely in their heads ever since.
According to the book cover flap of Joan Druett’s biography Tupaia: The Remarkable Story of Captain Cook’s Polynesian Navigator ( 2010 ):
As a man of high social ranking, Tupaia performed as an able intermediary, interpreting local rituals and ceremonies. Joseph Banks, the botanist with the expedition, is famous for his detailed, perceptive descriptions of the manners and customs of the Polynesian people. Much of the credit for this belongs to Tupaia. Not only did Tupaia become of the ship’s important artists, drawing lively pictures to illustrate what he described, but he could justly be called the Pacific’s first anthropologist.
In December 1770, Tupaia died of dysentery, contracted while the Endeavour was berthed for repairs in Batavia (modern-day Jakarta, Indonesia).