Einstein by Walter Isaacson was an excellent biography. While addressing the physics that drove Einstein's life, Isaacson presents the material in a readable and understandable manner. I really enjoyed this book.
Blood and Thunder by Hampton Sides is not a biography although it centers in many respects on the life of Kit Carson. It covers the period of early settlement in the Southwestern United States including John C. Fremont's march to California as well as the Navajo Wars. This is also one that I would highly recommend.