Humboldt, Baron Friedrich Heinrich Alexander von (1769–1859), a German scientist and explorer. The depth and range of Humboldt's investigations caused Ralph Waldo Emerson to call him “a universal man, one of those wonders of the world who appear from time to time as if to show us the possibilities of the human mind.” Cosmos (5 volumes, 1845–62), Humboldt's chief work, was a summary of the physical universe in which he tried to coordinate the whole of the scientific knowledge of his era.

Humboldt founded physical geography, comparative botany, and volcanology. He discovered the decrease in the earth's magnetic force from the poles to the Equator. He devised the isothermal lines used on maps of the world's climate. He discovered the Humboldt (or Peru) Current in the South Pacific Ocean along the coast of Chile and Peru. His studies of Peruvian guano resulted in its introduction as a fertilizer into Europe.

The foundation of Humboldt's fame was his five-year exploration of South America, Mexico, and Cuba, 1799–1804. He followed the Orinoco River to its source and discovered its connection with the upper Amazon system. He crossed the Andes Mountains of Ecuador and Peru five times, studying the distribution of plants as related to soil type and altitude. His studies of volcanoes in Ecuador and Mexico revealed their relationship to subterranean fractures in the earth's crust. He provided the first accurate information on rubber trees and on the cinchona tree (the source of quinine).

Humboldt returned to Europe with a collection of 60,000 pressed plants and 35 crates of insects, birds, rocks, and other specimens, most of which were new to science. His notes on this material and on his South American observations were eventually published in 30 volumes.

Humboldt was born in Berlin, the son of a Prussian nobleman. He studied the sciences under private tutors and at several German universities. He was never married. Humboldt devoted his personal fortune to his travels and research. He lived in Paris, 1808–27, and was in correspondence with most of the learned men of his time. In Humboldt's later years the patronage of Prussian kings—whom he served on various diplomatic missions—enabled him to continue his work and publish his books. In 1829 Humboldt made a geological exploration of central Asia for Czar Nicholas I of Russia.