Answer by taking a quote from the following article:

Cooper was born on May 7, 1901, in Helena, Montana to Alice (nee Brazier, 1873-1967) and Charles Henry Cooper (1865-1946). His father had emigrated from Houghton Regis, Bedfordshire and was a prominent lawyer, rancher, and (later) a Montana Supreme Court justice. His mother had emigrated from Gillingham, Kent and married Charles in Montana. In 1906, Charles purchased the 600-acre (240 ha) Seven-Bar-Nine cattle ranch about fifty miles (eighty kilometers) north of Helena near the town of Craig on the Missouri River.

For me the really satisfying things I do are offered me, free, for nothing. Ever go out in the fall and do a little hunting? See the frost on the grass and the leaves turning? Spend a day in the hills alone, or with good companions? Watch a sunset and a moonrise? Notice a bird in the wind? A stream in the woods, a storm at sea, cross the country by train, and catch a glimpse of something beautiful in the desert, or the farmlands? Free to everybody ...  Cooper's twenty-year friendship with Ernest Hemingway began at Sun Valley in October 1940. The previous year, Hemingway drew upon Cooper's image when he created the character of Robert Jordan for the novel For Whom the Bell Tolls. The two shared a passion for the outdoors, and for years they hunted duck and pheasant, and skied together in Sun Valley. Both men admired the work of Rudyard Kipling--Cooper kept a copy of the poem "If--" in his dressing room--and retained as adults Kipling's sense of boyish adventure. As well as admiring Cooper's hunting skills and knowledge of the outdoors, Hemingway believed his character matched his screen persona, once telling a friend, "If you made up a character like Coop, nobody would believe it. He's just too good to be true." They saw each other often, and their friendship remained strong through the years.  Cooper's social life generally centered on sports, outdoor activities, and dinner parties with his family and friends from the film industry, including directors Henry Hathaway, Howard Hawks, William Wellman, and Fred Zinnemann, and actors Joel McCrea, James Stewart, Barbara Stanwyck, and Robert Taylor. As well as hunting, Cooper enjoyed riding, fishing, skiing, and later in life, scuba diving. He never abandoned his early love for art and drawing, and over the years, he and his wife acquired a private collection of modern paintings, including works by Pierre-Auguste Renoir, Paul Gauguin, and Georgia O'Keeffe. Cooper owned several works by Pablo Picasso, whom he met in 1956. Cooper also had a lifelong passion for automobiles, with a collection that included a 1930 Duesenberg.  Cooper was naturally reserved and introspective, and loved the solitude of outdoor activities. Not unlike his screen persona, his communication style frequently consisted of long silences with an occasional "yup" and "shucks". He once said, "If others have more interesting things to say than I have, I keep quiet." According to his friends, Cooper could also be an articulate, well-informed conversationalist on topics ranging from horses, guns, and Western history to film production, sports cars, and modern art. He was modest and unpretentious, frequently downplaying his acting abilities and career accomplishments. His friends and colleagues described him as charming, well-mannered, and thoughtful, with a lively boyish sense of humor. Cooper maintained a sense of propriety throughout his career and never misused his movie star status--never sought special treatment or refused to work with a director or leading lady. His close friend Joel McCrea recalled, "Coop never fought, he never got mad, he never told anybody off that I know of; everybody that worked with him liked him."

Did he have any particularly famous friends?
Cooper's twenty-year friendship with Ernest Hemingway