V. K. Wellington Koo (29 January 1888 – 14 November 1985), whose Chinese name is variously romanized as Koo Vi Kyuin, Ku Wei-chün, and Gu Weijun, was a Chinese diplomat from the Republic of China. He was one of China's representatives at the Paris Peace Conference of 1919; served as an Ambassador to France, Great Britain and the United States; was a participant in the founding of the League of Nations and the United Nations; and sat as a judge on the International Court of Justice in The Hague from 1957 to 1967. Between October 1926 and June 1927, while serving as Minister of Foreign Affairs, Koo briefly held the concurrent positions of acting Premier and interim President of the Republic of China. Koo was the first and only Chinese head of state known to use a Western name publicly.

Born in Shanghai in 1887, Koo attended Saint John's University, Shanghai, and Columbia College, where he was a member of the Philolexian Society, a literary and debating club, and graduated in 1908. In 1912 he received his Ph.D. in international law and diplomacy from Columbia University.

Koo returned to China in 1912 to serve the new Republic of China as English Secretary to President Yuan Shikai. In 1915, Koo was made China's Minister to the United States and Cuba. In 1919, he was a member of the Chinese delegation to the Paris Peace Conference, led by Foreign Minister Lu Zhengxiang(Lou Tseng-Tsiang). Before the Western powers and Japan, he demanded that Japan return Shandong to China. He also called for an end to imperialist institutions such as extraterritoriality, tariff controls, legation guards, and lease holds. The Western powers refused his claims and, consequently, the Chinese delegation at the Paris Peace Conference was the only nation that did not sign the Treaty of Versailles at the signing ceremony.

Koo also was involved in the formation of the League of Nations as China's first representative to the newly formed League. From 1922, Koo served successively as Foreign Minister and Finance Minister. He was twice Acting Premier, in 1924 and again in 1926 during a period of chaos in Beijing under Zhang Zuolin in 1926-7. Koo was Acting Premier from 1 October 1926 and acted concurrently as Interim President. He served as Premier from January until June 1927, when Zhang organised a military government and Koo resigned. After the Northern Expedition toppled the government in Beijing in 1928, he was briefly wanted for arrest by the new Nationalist government in Nanjing, but through Zhang Xueliang's mediation he was reconciled with the new government and returned to the diplomatic service. He represented China at the League of Nations to protest the Japanese invasion of Manchuria. He served as the Chinese Ambassador to France from 1936–1940, until France was occupied by Germany. Afterwards, he was the Chinese Ambassador to the Court of St James's until 1946. In 1945, Koo was one of the founding delegates of the United Nations. He later became the Chinese Ambassador to the United States and focused in maintaining the alliance between the Republic of China and the United States as the Kuomintang began losing to the Communists and had to retreat to Taiwan.

Koo retired from the Chinese diplomatic service in 1956. In 1956 he became a judge of the International Court of Justice in The Hague and served as Vice-President of the Court during the final three years of his term. In 1967, he retired and moved to New York City, where he lived until his death in 1985.

Koo's third wife was Oei Hui-lan (simplified Chinese: 黄蕙兰; traditional Chinese: 黃蕙蘭; pinyin: Huáng Huìlán; 1899–1992). She married Koo in Brussels, Belgium in 1921. (She was reportedly previously the wife of Count Wittingham or of Count Hoey Stoker.) Much admired for her adaptations of traditional Manchu fashion, which she wore with lace trousers and jade necklaces, Oei Hui-lan was one of the 42 acknowledged children of the Peranakan Chinese sugar magnate Oei Tiong Ham.[16] She wrote two memoirs: Hui-Lan Koo (Mrs. Wellington Koo): An Autobiography (written with Mary Van Rensselaer Thayer, Dial Press, 1945) and No Feast Lasts Forever (written with Isabella Taves, Quadrangle/The New York Times, 1975). Koo had two sons with her: Yu-chang Koo (1922–1975, also Wellington Koo, Jr.) and Fu-chang Koo (1923–1977, a.k.a. Freeman Koo).

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