Yamagata Aritomo (山県 有朋; April 22,1838–February 1,1922) was a Japanese military leader and politician, and the third (December 24, 1889–May 6, 1891) and 9th (1898–1900) Prime Minister of Japan. He was the first Prime Minister under the Meiji constitution and parliamentary system. His forces, armed with modern weaponry, defeated a rebellion led by Saigo Takamori in 1877. He was a talented garden designer and today the gardens he designed are known masterpieces of Japanese style gardens.

Yamagata was born in a lower-classed samurai Family of Hagi, the capital of Choshu-han. He went to Shokasonjuku, a private school run by Yoshida Shoin and studied Chinese thought. In 1863 he did a good job as a commander of Kihei-tai, a troop newly organized by Choshu-han. During the Boshin War he was appointed a staff officer.

In 1869 he went to Europe together with Saigo Tsugumichi under the govermental order to research military system of European Forces. After his return to Japan in 1870, Yamagata energeticly modernized the Japanese army, which he modeled after the Prussian army . The Japanese army began subsequently began a draft that same year. In 1873 he was appointed to the Lord of Army and continued to develop the Army. He founded the General Staff Office, which became the main source of his political power. He had the emperor Meiji write the Imperial Words giving to the military Forces as well. This document was considered the moral core of the Japanese Army until its end in 1945.

In 1883 he was apponted to the Lord Chancellor, the highest bureaucrat position in the system before the Meiji Constitution. He suppressed the Free Democratic Movement, requesting for participation to politics by people, and ordered the formation of the local administrative system, which would consist of city, county and prefectural systems.

Under the Meiji constitution he was apponted to the Prime Minister twice in 1889 and 1898. In 1891 he received the honor of Genro, or official elder stateman. He showed his leadership on military issues during the First Sino-Japanese War as the Surprime Commander of the First Army and Russo-Japanese War as the Chief Officer of the General Staff Office in Tokyo.　After the death of Ito Hirobumi he became the most influential person in Japan.

In the anime Rurouni Kenshin, Aritomo Yamagata briefly enters the story to invite Himura Kenshin to join the army, as Kenshin's combat skills are legendary. Kenshin declines the offer. Aritomo Yamagata is later assassinated by Seta Soujiro.

Preceded by: (first term) Kuroda Kiyotaka	Prime Minister of Japan 1889–1891, 1898–1900	Succeeded by: (first term) Matsukata Masayoshi
Preceded by: (second term) Okuma Shigenobu		Succeeded by: (second term) Ito Hirobumi

de:Aritomo Yamagata fr:Yamagata Aritomo ja:山県有朋 zh:山縣有朋