Alfred Russel Wallace, OM, FRS (8 January 1823 – 7 November 1913), was a British naturalist, explorer, geographer, anthropologist, and biologist whose work played a central role in the development of evolutionary theory. He is best known for independently proposing the principle of natural selection, which led Charles Darwin to publish his own theory in 1859.

Born into a poor family in Monmouthshire, Wallace received little formal education. Largely self-taught, he educated himself through reading and by attending public lectures in London from 1837 onwards. Trained initially as a surveyor (1838–1843), he developed an interest in botany and natural history, and while working as a teacher from 1844 became deeply influenced by the writings of Thomas Malthus, Charles Lyell, and Robert Chambers.

Between 1848 and 1852, Wallace travelled to the Amazon basin, collecting insects and other specimens for sale to British collectors. A later and far more extensive expedition to the Malay Archipelago (1854–1862) resulted in the collection of more than 125,000 specimens, forming one of the most important nineteenth-century natural history collections. During this period Wallace developed his ideas on species change and adaptation.

In 1858, while in Malaya, Wallace sent an essay outlining his theory of natural selection to Charles Darwin. On 1 July 1858, a joint paper presenting the independent conclusions of both men was read to the Linnaean Society of London. Wallace continued to work across a wide range of scientific disciplines, making lasting contributions to biogeography, evolutionary biology, and the study of species distribution. His work remains central to the history of natural history and evolutionary thought.