Tom George Longstaff (15 January 1875 – 27 June 1964) was an English doctor, explorer and mountaineer, most famous for being the first person to climb a summit of over 7,000 meters in elevation, Trisul, in the Indian Himalaya in 1907. He also made important explorations and climbs in Tibet, Nepal, the Karakoram, Spitsbergen, Greenland, and Baffin Island. He was president of the (British) Alpine Club from 1947 to 1949 and a founding member of The Alpine Ski Club in 1908.