Sengoku Kotaro (千石興太郎; February 7, 1874 - August 22, 1950) was a Japanese political activist and union organizer in the early-mid 20th century. Born on the outskirts of Tokyo, he attended the Sapporo Agricultural College (now part of Hokkaido University) and after graduation took a job with the Ministry of Agriculture and Commerce guiding farmers in Shimane Prefecture, near Hiroshima, and then took a similar position in the South Seas Agency (Japanese Mandate over former German colonies in Oceania). He became deeply interested in the potential of agricultural and industrial cooperatives and unions, and took on leading roles in the Central Union of Co-operative Societies (産業組合中央會) and the National Federation of Purchasing Unions (国購買組合連合会). He published regularly in the monthly magazine Ie no hikari (家の光), the flagship publication of the Central Union of Co-operative Societies. Though Sengoku was highly influenced by socialism, his views on family and gender roles were traditional (as reflected in the publication's title), he was a strong advocate for the centrality of the imperial family in Japanese life, and he consistently advocated for imperial expansion, especially in China, in the 1930s. Late in life, Sengoku served as a cabinet minister, including as Minister of Agriculture in the brief government of Prince Naruhiko Higashikuni which oversaw the surrender of Japan to the Allies. After the war, he was deeply involved in organizing the Japan Cooperative Party (日本協同党) but was restricted from political participation by occupation authorities for his role in encouraging militarism and nationalism in the preceding years.