Koo Vi Kyuin (Chinese: 顧維鈞; pinyin: Gù Wéijūn; Wade–Giles: Ku Wei-chün; 29 January 1888 – 14 November 1985), better known as V. K. Wellington Koo, was a Chinese diplomat, politician, and statesman of the Republic of China.

Born in Shanghai, Koo studied at Columbia University in the United States, where he obtained a PhD in international law and diplomacy. On his return to China in 1912, he became Yuan Shikai's secretary for foreign affairs, and in 1919, was a member of China's delegation at the Paris Peace Conference, where he unsuccessfully demanded the return of Shandong. Between 1922 and 1927, Koo successively served the Beiyang government as minister of foreign affairs, minister of finance, acting premier, and president. After the Northern Expedition toppled the government in 1928, Koo joined the Nationalist government and continued his diplomatic career. In 1931, he represented China at the League of Nations to protest the Japanese invasion of Manchuria. He served as China's ambassador to France and Great Britain during World War II, and in 1945 represented China at the signing of the Charter of the United Nations. From 1946 to 1956, he served as the Republic of China's ambassador to the United States, and sat as a judge on the International Court of Justice in The Hague from 1957 to 1967. He retired in New York City and died at the age of 97.

Born in Jiading, now a suburb of Shanghai, in 1888, Koo grew up in an upper-class cosmopolitan family and was fluent in both English and French, which greatly aided his diplomatic career. In 1895, he was greatly affected by China's defeat at the hands of Japan in the First Sino-Japanese War, which led to the humiliating Treaty of Shimonoseki. Koo later wrote: "Ever since I was seven years old, when I heard with depressed heart the news of China's defeat by Japan, I had desired to work for China's recovery and the removal of the Japanese menace". Koo's father resolved to give him a "modern" education to help him prepare for the coming 20th century and to work for China's modernization. The naval battles during the recent war where the modern British-built warships of the Imperial Japanese Navy had blown out of the water the antiquated junks of the Imperial Chinese Navy had dramatically shown that modern, industrial powers had the advantage over backward nations. In 1897, Germany occupied the Shangdong Province after a short campaign, which again showed to the young Koo that as long as China was backward, it would be bullied by stronger powers.

Aged 11, Koo was sent to be educated at the Anglo-Chinese Junior College in Shanghai, where he was taught in English various subjects such as modern science and geography, though his studies were cut short when he contracted typhoid fever. While at the college, Koo once rode a bicycle down the streets of Shanghai into the International Settlement and followed an English boy also riding a bicycle onto the sidewalk, where an Indian policeman allowed the English boy to continue while stopping Koo to give him a fine for riding his bicycle on the sidewalk. Koo was shocked to discover that owing to extraterritoriality, the laws and rules that applied to Chinese in China did not apply to British subjects—in this instance, laws prohibiting riding a bicycle on the sidewalk—and that a foreign policeman had power over the Chinese police. Koo was left with a lifelong desire to end the status of extraterritoriality that had been imposed by the 19th-century "unequal treaties".

Koo studied at Saint John's University, Shanghai from 1901 to 1904, and Columbia University in New York City, where he was a member of the Philolexian Society, a literary and debating club, editor-in-chief of the Columbia Daily Spectator, and graduated with a B.A. in liberal arts (1908) and a M.A. in political science (1909). In 1912, he received his Ph.D. in international law and diplomacy from Columbia.

Koo returned to Beijing in 1912. He served the 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. In 1897, China had been forced to sign a treaty that gave a 99-year lease giving sovereignty over the city of Qingdao to Germany while also giving Germany various special rights and economic control over the Shandong peninsula. Qingdao became the principal German naval base in Asia. In 1914, Japan entered World War I on the Allied side and seized Qingdao after a siege. The Japanese made it very clear that they wished to take over the German rights in Shandong province by right of conquest, a demand that the Chinese vehemently rejected. In January 1915, Japan presented the 21 Demands that if accepted would have turned China into a virtual Japanese protectorate, warning in a note presented to the Chinese that Japan would take "vigorous methods" if the 21 Demands were rejected. Following protests from the United States that the 21 Demands would negate the Open Door policy towards trade with China, the Japanese dropped the more extreme of the 21 Demands. On 25 May 1915, the Japanese forced the Chinese to agree that after the war ended, the Japanese would take over all of the German rights in the Shandong peninsula, which caused protests all over China over what was deemed "National Humiliation Day".

As a young diplomat, Koo was strongly opposed to the acceptance of the Japanese demands. Koo had become close to President Woodrow Wilson, who invited him to visit the White House, where he was given to understand that the United States would support China's demands regarding the Shandong peninsula against Japan at the Paris Peace Conference. Wilson asked for Koo to attend the peace conference in Paris, and moreover, Koo travelled on the same ship that took Wilson and the rest of the American delegation to France in December 1918. The Canadian historian Margaret MacMillan wrote: "Koo, who was only thirty-two in 1919, was a forceful and distinguished personality...At Columbia University, in New York, where he earned an undergraduate and graduate degree, he had been an outstanding student...He had also been on the university debating team, as the Japanese delegates would learn to their cost".