Alfred Russell Wallace was an important evolutionary theorist in the 19th century. I found a good site dedicated to him at The Alfred Russel Wallace Website. It has details about Alfred Russel Wallace's life and work. It also includes a unique archive of images, FAQ's debunking some of the many myths surrounding Wallace and Darwin, plus information about the A. R. Wallace Memorial Fund and its projects. This is a nice history of science site worth checking out.
From the site:
Alfred Russel Wallace (1823 - 1913) was one of the 19th century's most remarkable intellectuals. His link to Charles Darwin as the co-discoverer in 1858 of evolution by natural selection would alone have secured his place in history, but he went on to make very many other significant contributions, not just to biology, but to subjects as far-ranging as glaciology, land reform, anthropology, ethnography, epidemiology, and even astrobiology. His pioneering work on evolutionary biogeography led to him becoming recognised as that subject’s ‘father’. Beyond this, Wallace is regarded as the pre-eminent collector and field biologist of tropical regions of the 19th century, and his book The Malay Archipelago (which was Joseph Conrad’s favourite bedside reading) is one of the most celebrated travel writings of that century and has never been out of print. Add to the above that Wallace was deeply committed to and a vocal supporter of spiritualism, socialism, and the rights of the ordinary person, and it quickly becomes apparent that he was a man with an extraordinary breadth of interests who was actively engaged with many of the big questions and important issues of his day.
By the time of his death Wallace was probably the world’s most famous scientist, but since then his intellectual legacy has been almost completely overshadowed by Darwin’s, largely thanks to the “Darwin Industry” of recent decades. This ‘industry’ has led to a highly “Darwinocentric” view of the history of modern biology, and as a result many of the important contributions made by Darwin’s contemporaries, like Wallace, are currently underestimated and undervalued.