The 26th President of the United States and a most brilliant, energetic, and individual character. He was the conservationist President. There is no doubt that he had a greater impact on land use and management in the United States than any other single individual.in American history, with the possible exception of Thomas Jefferson (1803 Louisiana Purchase). As Douglass Brinkley explains in his magisterial (but too long) biography of Roosevelt, The Wilderness Warrrior: Theodore Roosevelt and the Crusade for America (2009), p. 19: Roosevelt instituted the first national monuments and conservation commissions, quadrupled the number of national forest reserves, and established five national parks, among them the Grand Canyon. All told, he set aside for preservation more than 234 millions acres - approximately one in ten acres of the entire United States, Alaska included.
For a more general biography of Roosevelt, I would recommend Edmund Morris's two volumes, The Rise of Theodore Roosevelt (1979), which won the Pulitzer Prize, and Theodore Rex (2001).