The Greatest Knight: The Remarkable Life of William Marshal, the Power behind Five English Thrones by Thomas Asbridge (nonfiction 2014)

Humanity was lucky enough that someone found the only copy of Guillaime de Mareschal's biography, and this book uses that and other sources to reconstruct Marshal's long and amazing life.  It's a great read especially for non-fiction, even if you know nothing about the Angevin Empire.