The Prussian naturalist Alexander von Humboldt (1769–1859) is all around us. Yet he is invisible. “Alexander von Humboldt has been largely forgotten in the English-speaking world,” writes Andrea Wulf in her thrilling new biography. “It is almost as though his ideas have become so manifest that the man behind them has disappeared.” Wulf’s book is as much a history of those ideas as it is of the man. The man may be lost but his ideas have never been more alive.