British explorer and Arabist, the first European to cross the Rubʿ al-Khali, or Empty Quarter, of Arabia from east to west.

Philby was educated at Trinity College, Cambridge, and joined the Indian Civil Service in 1907. In 1917, as political officer of the Mesopotamian Expeditionary force, he was dispatched on a diplomatic mission to ʿAbd al-ʿAzīz ibn Saʿūd. After meeting with the future king of Saudi Arabia, he crossed the desert from Al-ʿUqayr to Jidda—an exploit recorded in his book, Heart of Arabia (1922). Philby succeeded T.E. Lawrence as chief British representative in Transjordan (1921–24) but resigned to establish a business in Arabia. He was an unofficial adviser of Ibn Saʿūd and converted to Islām in 1930.

After an unsuccessful foray into politics in England in 1939 and a brief incarceration there in 1940 because of his antiwar views, Philby returned to Arabia in 1945. Ten years later he was expelled because of his public criticism of the inefficiency and extravagance of the oil-enriched Saʿūdi regime. Philby made important contributions based on his Arabian explorations to the fields of archaeology, cartography, and linguistics. His son, Kim Philby, became a Soviet agent within the British intelligence service.