Baron Yamakawa Kenjiro (1854-1931) was a Japanese samurai of the late Edo-era who went on to become a noted physicist, university president, and author of several histories of the Boshin War. Though his name is commonly written "Yamakawa," he himself wrote it as "Yamagawa" in English.
Yamakawa was born as the third son to Yamakawa Naoe, a senior samurai of the Aizu clan. He became a member of the Byakkotai, a unit of the newly reorganized Aizu clan army composed mostly of boys aged 15 to 17 years, who fought in defense of Aizu during the Boshin War.
After the Meiji Restoration, through the mediation of the Zen monk Kawai Zenjun, Yamakawa was placed in the care of Choshu retainer Okudaira Kensuke. Yamakawa was sent by the new Meiji government to study physics at Yale University, where he was the first student from Japan to attend. On his return to Japan, he was posted to Tokyo Imperial University, and became Japanís first Japanese professor of physics in 1879. (There had already been several foreign professors, such as William Edward Ayrton.)
During the Meiji and Taisho-eras he helped found the Kyushu Institute of Technology in 1907 and served as president of Tokyo Imperial University (1901-1905 and 1913-1920), Kyushu Imperial University (1911-1913), and Kyoto Imperial University (1914-1915). He was later ennobled with the title of danshaku (baron) under the kazoku peerage system. Later in his life he was also a Privy Councilor (appointed in February 1923) and a member of the House of Peers.
He and his brother Yamakawa Hiroshi are known amongst historians of the late Edo-era as authors of two monumental texts - Yamakawa's being "Aizu Boshin Senshi," which catalogues the actions of his home clan during the war. He also authored several other history texts, including "Hoshu Aizu Byakkotai Jukyushi-den," which he wrote with fellow Aizu native Munekawa Toraji.