Gustav Spiller was a Hungarian-born ethical and sociological writer who was active in Ethical Societies in the United Kingdom. He helped to organize the First Universal Races Congress in 1911.
Gustav Storm was a Norwegian historian, a professor at the Royal Frederick University in Christiania from 1877. He was a driving force in the research of Scandinavian history and literature of the Middle Ages.
Gustav Struve, known as Gustav von Struve until he gave up his title, was a German surgeon, politician, lawyer and publicist, and a revolutionary during the German revolutions of 1848–1849 in Baden, Germany. He also spent over a decade in the United States and was active there as a reformer.