Biographies are one of the oldest types of historical writing and can be found in the literature of ancient Egypt, Greece, and Rome. They focus on the lives of important political and military leaders and, with the rise of Christianity, clerics and saints. A famous example from the late Renaissance period is Giorgio Vasari's Lives of the Artists (1550) which features dozens of biographies of well-known artists such as Leonardo da Vinci and Raphael. As the genre evolved in the modern period, biographies focused not only on the facts of a person’s life but also on their feelings and the overall historical context.

At over 1,000 pages, McCullough’s biography of Truman is extensive and thoroughly researched. The author relies on a variety of sources: personal correspondence, legal documents, newspapers, and other media, his own interviews, oral history, journals and diaries, military records, various types of official records linked to Truman’s political career, photographs, and even archeological artifacts such as a century-old recovered steamer with cargo. As the narrative heads into the 20th century, the information becomes more detailed and diversified. In contrast, the documentation about Truman’s ancestors from the pre-Civil War era is more limited.