Again we see there is nothing you can possess which I cannot take away.

Wiki:

Colonel Percy Harrison Fawcett (1867 – in or after 1925) was a British archaeologist and an explorer.

Along with his son, Fawcett disappeared under unknown circumstances in 1925 during an expedition to find what he believed to be an ancient lost city in the uncharted jungles of Brazil.

Percy Fawcett was born 1867 in Torquay, Devon, England to Edward B. and Myra Fawcett. His Indian born father was a Fellow of the Royal Geographic Society. Percy's elder brother Edward Douglas Fawcett (1866-1960) was a mountain climber, Eastern Occultist, and popular writer of adventure novels. In 1886 Percy received a commission in the Royal Artillery and served in Trincomalee, Ceylon where he also met his wife. Later he worked for the British secret service in North Africa and learned the surveyor's craft. He was also a friend of authors H. Rider Haggard and Arthur Conan Doyle, who used Fawcett's Amazonian field reports as an inspiration for The Lost World.

Fawcett's first expedition to South America was in 1906 when he travelled to Brazil to map a jungle area at the border of Brazil and Bolivia at the behest of the Royal Geographic Society; the society had been commissioned to map the area as a third party, unbiased by local national interests. He arrived in La Paz, Bolivia, in June. Whilst on the expedition, Fawcett claimed to have seen a giant anaconda, for which he was widely ridiculed by the scientific community. He reported other mysterious animals unknown to zoology, such as a small cat-like dog about the size of a foxhound, which he claimed to have seen twice.

Fawcett made seven expeditions between 1906 and 1924. He mostly got along with the locals through gifts, patience and courteous behaviour. In 1910 Fawcett made a trip to Heath River to find its source. Following his 1913 expedition, he supposedly claimed to have seen dogs with double noses - these may have been Double-nosed Andean tiger hounds. He returned to Britain for active service in the army during World War I, but after the war he returned to Brazil to study local wildlife and archaeology.

In 1925, with funding from a London-based group of financiers called The Glove, Fawcett returned to Brazil with his older son Jack for an exploratory expedition. Colonel Fawcett had studied ancient legends and historical records and was convinced a lost city existed somewhere in the Mato Grosso region, a city Fawcett named "Z." Fawcett left behind instructions stating that if his expedition to discover the lost city of Z did not return, no rescue expedition should be sent, lest the rescuers suffer his fate.

For a first-hand account of the encounter of Fawcett and his companions with the Kalapalo, told by a Kalapalo leader in Kalapalo to anthropologist Ellen Basso, please see Ellen Basso's The Last Cannibals (University of Texas Press)

The last sign of Fawcett was on May 29, 1925 when Fawcett telegraphed his wife that he was ready to go into unexplored territory only with Jack and Jack's friend Raleigh Rimmell. They were reported to be crossing the Upper Xingu, a south-eastern tributary of the Amazon River. Then nothing more was heard of them.

Many presumed that local Indians had killed them, several tribes being posited at the time – the Kalapalos who last saw them, or the Arumás, Suyás, or Xavantes tribes whose territory they were entering. Both of the younger men were lame and ill when last seen, and there is no proof they were murdered. It is plausible that they died of natural causes in the Brazilian jungle.

In 1927, a nameplate of Fawcett was found with an Indian tribe.

In June 1933, a theodolite compass belonging to Fawcett was found near the Baciary Indians of Matto Grosso by Colonel Aniceto Botelho ...

... Fawcett is said to have been an inspiration for Indiana Jones, the fictional archaeologist/adventurer, and a fictionalised version of Fawcett aids Jones in a novel. Also, according to an article in Comics Scene #45, he was also the inspiration of Kent Allard, the alter ego of the Shadow.

Arthur Conan Doyle also based his Professor Challenger character partly on Fawcett, and stories of the "Lost City of Z" became the basis for his novel The Lost World.