Who named the generation of ww1 veterans the lost generation?

The term "Lost Generation" was popularized by writer Gertrude Stein in the 1920s, who heard her French garage owner speak of his young auto mechanics as "une génération perdue" (a lost generation). The term later became associated with the disillusioned post-World War I generation of writers and artists, including Ernest Hemingway and F. Scott Fitzgerald.