German nationalist and political leader who turned the General German League (Allgemeiner Deutscher Verband), founded in 1891, into the militantly nationalistic and anti-Semitic Pan-German League (Alldeutscher Verband) in 1894.

A professor of statistics at Leipzig, Hasse represented the National Liberal Party in the Reichstag from 1893 to 1903. He served as the league's president from 1893 to 1908 and wrote the three-volume study Deutsche Politik (1905–07; “German Politics”) in which he made explicit the determination of the Pan-German movement: “We want territory, even if it be inhabited by foreign peoples, so that we may shape their future in accordance with our needs.”