Ulysses S. Grant has been the subject of scores of biographies, but his character has long remained elusive to historians. Even Grant’s closest friends found him hard to figure. General William T. Sherman noted that, despite having known Grant for decades, “to me he is a mystery, and I believe he is a mystery to himself.” Now, with unprecedented access to Grant’s collected works, Ronald C. White, Jr. has gotten closer to explaining the nature of the man who saved the Union.

American Ulysses: A Life of Ulysses S. Grant, released Tuesday, offers a novel interpretation of Grant, with White’s greatest departure from existing scholarship being his focus on Grant’s religion and marriage. Both of these, in White’s convincing analysis, explain more about Grant than earlier biographers realized.