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.

[3] 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.

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.

[15] Koo noted that under Wilson's 14 Points, the basis of the peace was to be national self-determination, which led him to argue that Japan had no right to the Shandong as its people were overwhelmingly Han and wanted to be part of China.

[16] Clemenceau described Koo as "a young Chinese cat, Parisian of speech and dress, absorbed in the pleasures of patting and pawing the mouse, even if it was reserved for the Japanese".

[19] Koo was greatly hurt when Lloyd George casually told him that China had made only the most "minimal" contributions to the Allied cause as he dismissed the work of the Chinese coolies in digging the trenches on the Western Front as unimportant.

[21] Koo's forceful advocacy of the Chinese case made him internationally famous while his status as a widower whose wife had just died of the "Spanish flu" conveniently ensured that he was free to marry again.

[23] On 4 May 1919, it was decided that the former German rights in the Shandong province would go to Japan, sparking the May Fourth Movement in China as hundreds of thousands of Chinese university students demonstrated against the decision.

Initially, Koo had planned to sign the Treaty of Versailles as long he could insert reservations stating his government was opposed to the Japanese gaining the German rights in the Shandong.

[42] Koo's two teenage sons embarrassed him by throwing deck chairs in a lake in a Paris park, and tried to claim diplomatic immunity when a French gendarme ordered them to stop.

[51] Koo felt it was in their own interests of Britain, France, the Soviet Union, and the United States to support China, and he was gravely disappointed when he discovered that his viewpoint was not as widely shared as he had assumed.

[53] In his appeal, Koo listed a number of war crimes committed by the Japanese, being careful to only quote from reports from Europeans and Americans in order to avoid accusations of bias.

[54] Speaking with great anger, Koo stated: "In Tianjin, the most crowded parts of the Chinese city were bombed by Japanese aeroplanes, killing hundreds of people for no other reason than to terrorize civilians.

The sight of mangled bodies and the cries of the maimed and wounded were so sickening to the hearts of the foreign Red Cross doctors that they voiced the fervent wish that the governments of the civilized Powers would make an effort to stop the carnage".

[56] Koo later wrote that as he watched from his train the still recovering French countryside that it "led me to reflect that although the youthfulness of the trees and the relative newness of the buildings still told the story of the war, the world had learned little from it.

[58] On 12 November 1937, Japan issued a statement firmly ruling out taking part in the Brussels conference and refused the offer of mediation, claiming that the war was a defensive struggle as the Japanese maintained that China was the aggressor.

[48] During the Sudetenland crisis of 1938, Koo favored having the idea of deterring Germany from invading Czechoslovakia by involving the League of Nations, whose charter called for "collective security" in the event of aggression.

[63] In July 1938 when the Treasury Secretary, Henry Morgenthau Jr., visited Paris, Bullitt introduced him to Koo, whom spoke about the need for American economic aid to China.

[64] Koo wrote that Chamberlain wanted to revive the 19th century Concert of Europe by creating an Anglo-German duumvirate that would "dominate and control the smaller and weaker powers".

[64] Koo argued that Chamberlain's attempts to create an Anglo-German dominated new Concert of Europe had finished off the League of Nations as a force in world politics and would have a disastrous impact on Anglo-Soviet relations, which had never been friendly to begin with.

[55] In June 1939, Koo discovered a senior Chinese diplomat, Huang Zheng, had been selling visas to Jewish refugees from Germany, Austria and Czechoslovakia.

[73] In July 1941, the Japanese occupied the southern half of French Indochina, giving Japan the ability to project air and naval power well into the South China Sea.

[76] The way that only four divisions of the Imperial Japanese Army who despite being outnumbered three to one by an Anglo-Indian-Australian force opposing them had been able to conquer Malaya and Singapore, billed at the time as the "Gibraltar of the East", in less than two months both astonished and shocked British officials.

[79] On 11 January 1943, Koo signed in London a new Sino-British treaty that saw Britain renounce all of its extraterritorial rights in China, through the British refused to return Hong Kong as the Chinese had wanted.

[81] Chiang also instructed Koo that his answers to the British protests regarding his statements were to state that China wanted India to be granted Dominion status, which he believed would lead to the Indians of their own choice continuing the war.

[82] Soong reported to Chiang that based on his talks with Eden and Koo that the British did not regard China as a serious military power and that Churchill was far interested in the war against Germany than with Japan.

[86] Koo stated he felt with the long-standing vexatious issue of extraterritorial rights finally settled in China's favor, it would be possible to make an alliance with the United Kingdom against the Soviet Union after the war.

[87] In the summer of 1944, Koo was contacted by agents of Charles de Gaulle, who wanted an agreement that China would support restoration of French rule in Indochina after the war.

[6] In an interview conducted in 1969 on the 50th anniversary of the Treaty of Versailles, Koo stated that the Paris peace conference, which launched the May 4th movement, was a turning point in Chinese views of the West as he observed that many Chinese intellectuals believed the victorious powers of 1918 would allow China to be treated as an equal, and the outcome of the Paris peace conference had turned public opinion against the Western powers.

[112][113] On September 3, 1959, Koo married his fourth wife Yen Yu-yun (1905–2017),[114] the widow of Clarence Kuangson Young, who had been his long-term mistress since the 1930s while her husband was still alive.