Short answers, pulled from the story.
Alexander von Humboldt was a German polymath whose quantitative work on botanical geography laid the foundation for biogeography, and whose advocacy for long-term geophysical measurement pioneered modern geomagnetic and meteorological monitoring. He and Carl Ritter are regarded as the founders of modern geography as an independent scientific discipline. He is also called "the father of ecology" and "the father of environmentalism".
Alexander von Humboldt traveled to the Americas between 1799 and 1804, sailing from La Coruna on the 5th of June 1799 with French botanist Aime Bonpland. They explored Venezuela, Cuba, Colombia, Ecuador, Peru, Mexico, and briefly the United States, returning to Europe when Humboldt landed at Bordeaux on the 3rd of August 1804.
In 1802, Humboldt and his party reached an altitude of 19,286 feet on Chimborazo, a record for any Westerner at the time, though it fell about 1,000 feet short of the summit. The climb also inspired his famous Chimborazo cross-section map, depicting temperature, altitude, humidity, and species distribution in a single illustration.
In 1800, while studying a rapid fall in the water level of Lake Valencia in Venezuela, Humboldt concluded scientifically that the clearing of tree cover was causing local climate change by removing shade, evaporation, and radiation. He described similar human-induced environmental impacts again in 1831. These observations make him one of the earliest scientific writers to document the local effects of land use on climate.
Kosmos is Alexander von Humboldt's multi-volume work attempting to unify all branches of scientific knowledge into a single account of the universe, developed from public lectures he delivered at the University of Berlin in the winter of 1827-1828. The first two volumes were published between 1845 and 1847; the final posthumous fragment appeared in 1862. It was translated into multiple languages and was extremely popular in Britain and America.
Scholars point to three reasons for Humboldt's declining renown. First, the trend toward academic specialization made his wide-ranging generalist approach seem outdated. Second, his literary style, once celebrated, came to be criticized as overly ornate. Third, rising anti-German sentiment in the late 1800s and early 1900s in the United States eroded his reputation in the countries where he had been most celebrated.