surgeon and sociologist whose writings on the behaviour of man in the mass popularized the phrase herd instinct. A surgeon at University College Hospital, London, from 1906, and professor of surgery there from 1935, Trotter held the office of honorary surgeon to King George V from 1928 to 1932. In the history of surgery he is especially noted for his work on the regeneration of sensory nerves in the skin.

As early as 1908 Trotter began to publish articles on herd behaviour and its predictability in gregarious animals, including man. His Instincts of the Herd in Peace and War (1916; 2nd ed., 1919, reissued 1953) was written during World War I and revised in the light of wartime socio-psychological developments.