Robert Peter Fleming (31 May 1907 – 18 August 1971) was a British adventurer, journalist, soldier and travel writer. He was the elder brother of Ian Fleming, creator of James Bond, and attained the British military rank of Lieutenant Colonel.

Peter Fleming was one of four sons of the barrister and Member of Parliament (MP) Valentine Fleming, who was killed in action during World War I in 1917, having served as MP for Henley from 1910. Fleming was educated at Durnford School and at Eton, where he edited the Eton College Chronicle. The Peter Fleming Owl (the English meaning of "Strix", the name under which he later wrote for The Spectator) is still awarded every year to the best contributor to the Chronicle. He went on from Eton to Christ Church, Oxford, and graduated with a first-class degree in English.

Fleming was a member of the Bullingdon Club during his time at Oxford. On 10 December 1935 he married the actress Celia Johnson (1908–1982), best known for her roles in the films Brief Encounter and The Prime of Miss Jean Brodie.

In April 1932 Fleming replied to an advertisement in the personal columns of The Times: "Exploring and sporting expedition, under experienced guidance, leaving England June to explore rivers central Brazil, if possible ascertain fate Colonel Percy Fawcett; abundant game, big and small; exceptional fishing; room two more guns; highest references expected and given." He then joined the expedition, organised by Robert Churchward, to São Paulo, then overland to the rivers Araguaia and Tapirapé, heading towards the last-known position of the Fawcett expedition.

During the inward journey the expedition was riven by increasing disagreements as to its objectives and plans, centred particularly on its local leader, whom Fleming disguised as "Major Pingle" when he wrote about the expedition. Fleming and Roger Pettiward (a school and university friend recruited onto the expedition as a result of a chance encounter with Fleming) led a breakaway group.

This group continued for several days up the Tapirapé to São Domingo, from where Fleming, Pettiward, Neville Priestley and one of the Brazilians hired by the expedition set out to find evidence of Fawcett's fate on their own. After acquiring two Tapirapé guides the party began a march to the area where Fawcett was reported to have last been seen. They made slow progress for several days, losing the Indian guides and Neville to foot infection, before admitting defeat.

The expedition's return journey was made down the River Araguaia to Belém. It became a closely fought race between Fleming's party and "Major Pingle", the prize being to be the first to report home, and thus to gain the upper hand in the battles over blame and finances that were to come. Fleming's party narrowly won. The expedition returned to England in November 1932.

Fleming's book about the expedition, Brazilian Adventure, has sold well ever since it was first published in 1933, and is still in print.^{[as of?]}