Harry St John Bridger Philby, CIE (3 April 1885 – 30 September 1960), also known as Jack Philby or Sheikh Abdullah (Arabic: الشيخ عبدالله), was a British Arabist, advisor, explorer, writer, and a colonial intelligence officer who served as an advisor to King Abdulaziz ibn Saud, the founder of Saudi Arabia.
As he states in his autobiography, he "became something of a fanatic" and in 1908 "the first Socialist to join the Indian Civil Service". After studying Oriental languages at the University of Cambridge, he was posted to Lahore in the Punjab in 1908, acquiring fluency in Urdu, Punjabi, Baluchi, Persian and eventually Arabic. He converted to Islam in 1930 and later became an adviser to Ibn Saud, urging him to unite the Arabian Peninsula under Saudi rule, and helping him to negotiate with the United Kingdom and the United States when petroleum was discovered in 1938. His second marriage was to a Saudi Arabian woman, Rozy al-Abdul Aziz.