Andrea Wulf, a historian who has written on gardens and scientific exploration, resurrects Alexander von Humboldt, the nineteenth-century naturalist who was once the most famous scientist in the world but has largely faded from English-speaking consciousness. Humboldt's five-year expedition through Latin America in 1799-1804 produced observations that transformed multiple sciences, but his greater contribution was conceptual: he developed a vision of nature as a web of interconnected forces rather than a collection of discrete objects to be classified. This holistic understanding, which Humboldt called 'Cosmos,' laid the foundation for modern ecology and environmentalism. Wulf traces Humboldt's life from his Prussian childhood through his explorations, his decades of writing in Paris, and his influence on figures from Simon Bolivar to Charles Darwin to Henry David Thoreau. She examines how Humboldt's ideas about nature's interconnection led him to recognize human damage to the environment and to connect environmental destruction with colonialism and slavery. The book argues that Humboldt's approach, which combined scientific rigor with aesthetic appreciation and political awareness, remains essential for confronting contemporary environmental challenges. Richly researched and compellingly written, this biography not only restores an important figure to visibility but demonstrates the continuing relevance of his way of seeing the natural world.