Kathleen Dalton, a high school history teacher, has dedicated her entire life to the study of Theodore Roosevelt. This scholarly biography is on its way to becoming the new one-volume standard. As far as "standard bios" go this one's not that long—over 500 pages—but it'll take you some time to get through.
This is the book that Dalton's book is replacing. Almost from its publication, William Harbaugh's biography of Roosevelt has been the one book on Roosevelt to read. It's good, and just about as long as Dalton's. You're not going to get much from reading Dalton and Harbaugh, but if you really want to know about T.R., reading one or the other isn't a bad idea.
If you really want to learn about T.R., these are the books to start with. Edmund Morris is writing what is already being called the definitive study of Theodore Roosevelt, and he's not even done yet. Two of the projected three volumes have already appeared, covering T.R.'s life from his birth through the end of his presidency. The first volume won the Pullitzer Prize. Both books are well written and thoroughly researched.
David McCullough is a consummate story-teller, and, in this study of the young T.R., he puts all his gifts on display. McCullough focuses on T.R.'s coming of age. Although more than a quarter century old, the book is still widely read. It won the National Book Award back when it first came out.
Throughout his life, T.R. was guided by some pretty strange ideas about muscular Christianity, the corrupting influence of modern society, and the need to recapture virile American masculinity. In this groundbreaking book, historian T.J. Jackson Learns explores where those ideas came from, why they emerged when they did, what they meant, and what kind of power they had. It's a modern classic of social and intellectual history. Make sure to read the first chapter carefully.
What can we say? Roosevelt still makes great copy. In this New York Times Notable Book, Candice Millard tells the story of T.R.'s ill-fated and deadly 1912 Brazilian expedition. It's a best seller, and with good cause: the story is gripping, unbelievable, and completely true.