Long overshadowed by his contemporaries Charles Darwin and Thomas H. Huxley, Alfred Russel Wallace was an English naturalist and pioneer evolutionist who researched biological diversity through extensive exploration and travel. Independent of Darwin, Wallace developed a theory of evolution through natural selection, which ultimately spurred Darwin to complete and publish his own Origin of Species. Famous for drawing Wallace's Line, the boundary line separating the Asian and Australian zoological regions, Wallace's studies of the distribution of plants and animals pioneered an evolutionary approach to global and island biogeography. This study reintroduces Wallace to a general readership beyond the cadre of scientists and historians familiar with his work.