Who is Nick Adams from The Nick Adams Stories and what is their importance?

Nick is the central character in all of the short stories in the collection. As the preface notes, Nick is largely a biographical creation, but his life should not be taken to strictly mirror Hemingway's. It should be noted that Nick's story is not coherent or continuous through these stories, indicating that he perhaps served as more of a vehicle for exploring a topic or situation than as a literary creature who was supposed to stand wholly on his own. For example, Nick goes crazy from a poorly treated head wound in "The Way You'll Never Be," but all stories taking place later in life depict him as perfectly sane. Likewise, Littless, his sister who features in "The Last Good Country," is never mentioned (at least by name) in any other stories.