[4] Cooper's biographer and longtime partner John Richardson considered his suffering from the social exclusion of his family by his countrymen to be a defining characteristic of his friend, explaining in particular his Anglophobia.
When he was 21, he inherited £100,000 (then about US$500,000, a significant fortune), enabling him to study art history at the Sorbonne, in Paris and at the University of Freiburg in Germany, which was not possible at the time in Cambridge.
At the outbreak of the Second World War in 1939, he had acquired 137 cubist works, partly with the help of the collector and dealer Gottlieb Reber (1880–1959),[5][9] some of them masterpieces, using a third of his inheritance.
[10][11] Cooper was not eligible for regular military service, due to an eye injury, so he chose to join a medical unit in Paris when World War II started, commanded by the art patron Etienne de Beaumont, who had commissioned works by Picasso and Braque, among others.
Back in Liverpool Cooper was arrested as a spy because of his French uniform, missing papers and improper behaviour, treatment for which he never forgave his fellow countrymen.
Subsequently, he joined the Royal Air Force Intelligence unit and was sent to Cairo as an interrogator, a job at which he was enormously successful in squeezing out secrets from even hard-boiled prisoners, not least due to his "'evil queen' ferocity, penetrating intelligence, and refusal to take no for an answer, as well as his ability to storm, rant, and browbeat in Hochdeutsch, dialect, or argot, [which] were just the qualifications that his new job required.".
[14] He was very successful, his most eminent discovery being the Schenker Papers which made it possible to prove that Paris dealers, Swiss collectors, German experts and museums, in particular the Museum Folkwang in Essen were deeply engaged in looting Jewish property and entartete Kunst as well as building collections for Hitler and Hermann Göring (Schenker was the transport company shipping art to Germany, having excellent bookkeeping)[15][16] Equally amazing to MFAA investigators[14] was his detailed research on the Swiss art trade during the war; it turned out that many dealers and collectors had been involved in trading looted art.
[5][17] After the Second World War, Cooper returned to England, but could not settle in his native country and moved to southern France, where in 1950 he bought the Château de Castille near Avignon, a suitable place to show his impressive art collection, which he continued to expand with newer artists such as Klee and Miró.
Cooper published frequently in The Burlington Magazine and wrote numerous monographs and catalogues about artists of the 19th century, including Degas, van Gogh and Renoir, but also about the Cubists he collected.
[27] Cooper not only contributed to The Burlington Magazine as an author, but also served on its board of directors and held shares; he nevertheless tried to force the editor, Benedict Nicolson, to resign, unsuccessfully.
[31][32] In 1961, Cooper was found on a road outside Nîmes, heavily injured by stab wounds in the stomach; on his way to the post office in Nîmes to send an article about Picasso's birthday to a London newspaper, he had stopped at a notorious quarter and picked up a young Algerian Fellagha (resistance fighter against the French occupation forces) who had been interned in an open camp nearby.
[33][34] In 1974, about 20 small paintings by Picasso, Braque and Gris were stolen from his house; Cooper dismissed his old housekeeper and in consequence lost the respect of his neighbours.
In a letter to the editor of The Times, he declared in 1980: I can see nothing in the work of any British artist of the twentieth century which obliges me – judging of course, by international and eternal standards of achievement – to recognize a major creative talent.
To my eyes, the work of all of them seems mediocre, uninspired and not particularly competent.Towards the end of his life, he was honoured by being appointed the first foreign patron of the Museo del Prado in Madrid, which made him very proud.