Captain William Henry Irvine Shakespear (1878-1915) is one of the lesser-known Britons to have lived in the Arabian Gulf. However, his regional knowledge and influence were considerable and had the potential to change the course of Arab-British relations, which they indeed did despite his short lifetime. This paper will attempt to show that his diplomatic endeavours deserve considerably more credit and recognition than they have hitherto been afforded. Born in Bombay, Shakespear graduated from Sandhurst in 1897, serving in the British and Indian Armies and learning Urdu, Pushtu, Farsi and Arabic to interpreter level. At only twenty-five, he was posted first as consul to Bandar Abbas and then to Kuwait, where, in 1910, he met 'Abd Al-'Aziz Al Sa'ud, better known as Ibn Sa'ud, the future king of Saudi Arabia, and built a strong personal relationship with him (Harrigan, 2008). Shakespear immersed himself in the local dialect and culture, becoming expert in riding, falconry and hunting with salukis. His humanitarian personality and diverse interests such as photography and botany conceivably helped him form friendships and negotiation skills. His extensive desert travel enabled him to provide unique and crucial intelligence to London; he tried to persuade Britain to support 'Abd Al-'Aziz, then Emir of Riyadh, correctly perceiving him as a future leader, but it was currently negotiating the Anglo-Ottoman treaty and rejected Shakespear’s counsel. The Turks held part of the Arabian coast and, while 'Abd al-'Aziz aimed to expel them, the British hoped they could advance British regional interests. However, when the Turks indicated their allegiance to Germany before World War I, London again approached Shakespear for advice (Dillon, 2019). In 1915, he began work with 'Abd Al-'Aziz on a draft treaty which would recognise him as the independent ruler of Najd (Harrigan, 2008). 'Abd Al-'Aziz was then engaged in hostilities with Ibn Rashid, his rival for Najd, and entered into battle with his army at Jarrad. Shakespear remained, despite 'Abd Al-'Aziz’s misgivings, and, prominent in his English uniform, was fatally shot by the enemy. Nevertheless, the Anglo-Saudi Treaty was signed on 26 December 1915 (Lowe, n.d.), mainly through his efforts. His success was, however, overshadowed by the subsequent exploits of T. E. Lawrence and others. Philby (1930) comments that Shakespear’s death is among “individual events which have changed the course of history,” and Plumbly (n.d.) adds that for those working on relations between Britain and Saudi Arabia, “he remains a hero.”