Gustav Landauer was one of the leading theorists on anarchism in Germany at the end of the 19th and the beginning of the 20th century. He was an advocate of social anarchism and an avowed pacifist.

Gustav Leopold Plitt (27 March 1836, Genin, near Lübeck – 10 September 1880, Erlangen) was a German Protestant theologian.

Gustav Mann (1836–1916) was a German botanist who led expeditions in West Africa and was also a gardener at the Royal Botanic Gardens, Kew.

Gustav Meyrink was the pseudonym of Gustav Meyer, an Austrian author, novelist, dramatist, translator, and banker, most famous for his novel The Golem. He has been described as the "most respected German language writer in the field of supernatural fiction".

Gustav Naan was an Estonian physicist and philosopher. According to the Estonian Encyclopedia's definition, he "wrote plenty of irritating publicist articles".

Gustav Orreus (1738–1811) was a doctor of Finnish-Swedish origin in the Imperial Russian service. An early epidemiologist, Orreus distinguished himself during the Russian plague of 1770–72. He was the first Doctor of Medicine ever to qualify in Russia.

Gustav Friedrich Konstantin Parthey was a German philologist and art historian.

Theodor Gustav Pauli was a German art historian and museum director in Bremen and Hamburg.

Gustav Pfizer (1807–1890) was a German poet and critic of the Swabian school.

Gustav Pfleger Moravský was a Czech novelist, poet and dramatist. He is generally associated with the Májovci, but was not actually a member of that group.