Henry Adams
Henry Adams, of course, is the author of the book. Although he does not include many personal details in his work, he does emphasize things that are important in his life that may not be considered important to others. Adams delivers a clear bias in his work, as he leaves out things that he didn't have time to add, didn't feel were important, or he was too embarrassed to include.
Clarence King
Clarence King was an American geologist born in 1942 who was instrumental in the American Geological Survey of the western portion of the United States. King is repeatedly mentioned by Adams, as they were personal friends. He adds that the work that King did was important to the expansion of America as a whole, and should be included in how the country became more centralized. King was in the last era of explorers that was able to explore land that was previously unexplored.
John Milton Hay
Hay was another one of Adam's close friends, whom Adams mentions throughout the autobiography. Hay was a Secretary of State under William McKinley, and served as an assistant to President Lincoln. Adams explains how the role of someone in government, like Hay, has become more important with time. For example, it used to be easy to obtain such a position - many earlier presidents were poor. Now, with the advances in science and technology and a growing population, maintaining such a position has become much harder.
