Ernest Hemingway was not only a commanding figure in 20 th -century literature, but was also a pack rat .He saved even his old passports and used bullfight tickets, leaving behind one of the longest paper trails of any author. “Ernest Hemingway: Between Two Wars,” which opens on Friday at the Morgan Library & Museum, is the first major museum exhibition devoted to Hemingway and his work. The largest and most interesting section focuses on the ’20s, Hemingway’s Paris years, and reveals a writer we might have been in danger of forgetting: Hemingway before he became Hemingway . The exhibition does not fail to include pictures of the bearded, manly, Hem.He’s shown posing with some kudu he has just shot in Africa and on the bridge of his beloved fishing boat, the Pilar, with Carlos Gutiérrez, the fisherman who became the model for “The Old Man and the Sea.” But the first photo the viewer sees is a big blowup of a handsome, clean-shaven, 19-year-old standing on crutches. This is from the summer of 1918, when Hemingway was recovering from wounds at the Red Cross hospital in Milan and trying to turn his wartime experiences into fiction. The evidence at this exhibition suggests that, in the early days, he often wrote in pencil, mostly in cheap notebooks but sometimes on whatever paper came to hand. The first draft of the short story “Soldier’s Home” was written on sheets he appeared to have snatched from a telegraph office. The impression you get is of a young writer seized by inspiration and sometimes barreling ahead without an entirely clear sense of where he is going. F. Scott Fitzgerald (some of whose letters with Hemingway is also on view) famously urged him to cut the first two chapters of “The Sun Also Rises,” complaining about the “elephantine facetiousness” of the beginning, and Hemingway obliged, getting rid of a clunky opening that now seems almost “meta”. In 1929, in a nine-page penciled critique, Fitzgerald also suggested numerous revisions for “A Farewell to Arms.” Hemingway took some of these, but less graciously, and soon afterward his friendship with Fitzgerald came to an end. The papers at the Morgan show a Hemingway who is not always sure of himself. There are running lists of stories he kept fiddling with, and there are lists and lists of possible titles, including the 45 he considered for “Farewell” and 47 different endings for the novel. In display case after display case, you see Hemingway during his Paris years inventing and reinventing himself, discovering as he goes along just what kind of writer he wants to be. In a moving 1925 letter to his parents, who refused to read “In Our Time,” his second story collection, he writes: “You see I’m trying in all my stories to get the feeling of the actual life across — not just to describe life — or criticize it — but to actually make it alive. So that when you have read something by me you actually experience the thing. You cant do this without putting in the bad and the ugly as well as what is beautiful.” By the time the Second World War broke out, Hemingway had solidified into the iconic figure we now remember: Papa. Even J. D. Salinger calls him this. And a blustery, cranky Hemingway appears in 1949 when aboard the Pilar he grabs an old fishing diary and begins scrawling an angry letter to Harold Ross, the editor of The New Yorker, complaining about Alfred Kazin’s review of “Across the River and Into the Trees,” not, in truth, a very good book. But, Hemingway, often drinking and depressed, didn ’ t know it, his best work was behind him by then.