william forbes was born on november 25, 1837 in new york, united states to the forbes family. he was the eldest son of paul siemen forbes (1808–86), who travelled to china in 1857 joined his cousin john murray forbes who had been heavily involved in china trade and served as partner in russell & co., prominent american trading firm in the far east, and as the united states consul in canton. william had two younger brothers, henry de courcy forbes (1849–1920) and paul revere forbes (1860–1936).