"I'm no orator," Theodore Roosevelt once said, "and in writing I'm afraid I'm not gifted at all. … If I have anything at all resembling genius it is the gift for leadership."

There was nothing attractive about Roosevelt. He stood no taller than five feet, nine inches, and was built like a barrel. His blue eyes squinted out nearsightedly through pince-nez, and his brown mustache framed teeth so large and white they sometimes frightened friends as well as enemies. His voice was high-pitched, even squeaky.

Yet, the vivid force of his character and personality, his unabashed, contagious joy in taking charge made the difference. He was a leader of monumental proportions. A political foe called him "a steam-engine in trousers." A British visitor thought him comparable only to Niagara Falls among the natural wonders of the New World. His ability to lead—and the rugged, restless, constitution that went along with it—was not really a gift at all, but a hard-won achievement. To ...