Some day someone will write the definitive biography of Sir Wilfred Thesiger, perhaps the 20th century's greatest explorer but also a complicated enigma. This book, however, is not that biography. It is a pictorial volume celebrating his achievements and reproducing nearly 200 of his photographs, some of them previously unpublished. It is a pleasing retrospective with an outstanding introduction. But there is more to Thesiger than this slender book can reveal.

He was born in 1910 at the British Legation in Addis Ababa, and he spent his early years in what was then Abyssinia. He was sent to England to be educated at prep school, then Eton and Oxford University, before joining the Sudan political service in 1935. It was at Eton that he discovered T.E. Lawrence's Revolt in the Desert , the popular abridgement of the privately printed Seven Pillars of Wisdom . Both books were to introduce Thesiger to an involvement with Arabia that influenced the rest of his life.

In 1933, he became the first European to cross the forbidden interior of Aussa in Danakil country to discover how and where the Awash River ended.

Thereafter, Thesiger twice crossed the Empty Quarter in Arabia (a journey dismissed as impossible by Lawrence) and explored the interior of Oman. For eight years from 1950 he lived in southern Iraq with the Marsh Arabs and travelled also in Kurdistan, Morocco and the Karakoram and Hindu Kush ranges in western Asia. From 1978, he spent most of his time with the Samburu tribes in northern Kenya before returning to England in 1994. He died in Surrey in August 2003. He never married.

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Using only a damaged Kodak box camera discarded by his father, Thesiger took some excellent photographs of the Danakil and their country. Then in 1932 or 1933 he bought his first 35mm Leica. With this he took some fine photographs in the Sudan, but the vast majority of his best photographs were shot in Arabia, Iraq and western Asia after the Second World War.

(During the war he served in Abyssinia, the Middle East and North Africa.) Alexander Maitland comments: "In 1938 Thesiger had not yet acquired the techniques which he exploited so successfully in later years: getting as close as possible to subjects for intimate portraiture, either kneeling or squatting down to photograph people or objects at an upward angle, with the sky as a neutral background." Nevertheless, in the late 1930s, he pre-empted German film-maker Leni Riefenstahl by photographing Nuba wrestlers in Africa - among the few action photographs he ever took.

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The quality of Thesiger's photography had improved substantially a decade later, and most of his superb Arabian photographs appeared in his two best books, Arabian Sands (1959) and The Marsh Arabs (1964). Maitland compares and contrasts Thesiger's relationship to travel photography with that of the Orientalist painters to painting. He speculates that the painter and eclectic Jacques Majorelle would have "found it ironic that Thesiger, an empathist of Orientalism, identified himself with photography, since it had been the camera's increasing precision and popularity that led to the decline of Orientalist art". He adds that "the artists' sensual voyeuristic preference for Eastern bathing scenes and shapely odalisques has been replaced, for Thesiger, by tribal ceremonies and photogenic warriors".

Although Thesiger photographed landscapes and buildings, he admitted in Arabian Sands that it was portraits of remote peoples that were his favourite subject.

As a photographer, Thesiger was always an amateur with an excellent eye - no Alfred Eisenstaedt or Henri Cartier-Bresson. In fact, his photographs are similar to those of Swiss-born Werner Bischof in 1951 of the prisoner-of-war camps in South Korea, and of famine in Bihar, India, and those of Indian photographer Kishor Parekh, who recorded the bloody emergence of independent Bangladesh in 1971. Like them, Thesiger strove to portray his human subjects with dignity. His archive of more than 30,000 photographs, which he donated to Oxford's Pitt Rivers Museum, is an invaluable record of tribes, ceremonies, landscapes, dwellings and peoples on the point of extinction or who no longer exist.

Thesiger was never commercially minded, and he never travelled for the sole purpose of writing a book. His grandmother left him a substantial annuity that ensured his independence and added to his "arcane charisma". According to his own estimate, by 1970 he had walked more than 40,000 miles - twice the circumference of the globe - and had become one of the century's minor icons. Concluding his introduction, Maitland notes: "While it is true that Thesiger was inclined to be temperamental... had he been less determined, ruthless, or self-centred, it is unlikely that he would have achieved his greatest aims as an explorer and a traveller." As any restless voyager will tell you, it is the accident of discovery that propels the true adventurer; and the stimulation of achievement that drives the explorer. This book is a tribute to a man to whom "challenge gave an undiminished zest for living".

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Christopher Ondaatje is a council member, Royal Geographical Society, and author of Journey to the Source of the Nile .