Wilfred Batten Lewis Trotter, FRS (3 November 1872 – 25 November 1939) was an English surgeon, a pioneer in neurosurgery. He was also known for his studies on social psychology, most notably for his concept of the herd instinct, which he first outlined in two published papers in 1908, and later in his famous popular work Instincts of the Herd in Peace and War, an early classic of crowd psychology. Trotter argued that gregariousness was an instinct, and studied beehives, flocks of sheep and wolf packs.