Hamaguchi Osachi was a Japanese politician, cabinet minister and Prime Minister of Japan from 1929 to 1931. Nicknamed the "Lion Prime Minister" due to his dignified demeanor and mane-like hair, Hamaguchi served as leading member of the liberal Rikken Minseitō during the "Taishō democracy" of interwar Japan. He was a member of the House of Representatives from 1915 until his death. He initially survived an assassination attempt by a right-wing extremist in 1930, but died about nine months later from a bacterial infection in his unhealed wounds.

Rikken Minseitō was one of the main political parties in pre-war Empire of Japan. It was commonly known as the Minseitō.