Charles Darwin is the famous scientist known for popularizing the theory of evolution in the 19th century. His groundbreaking work, "On the Origin of Species," published in 1859, introduced the concept of natural selection as a mechanism for evolution. Darwin's extensive observations during his voyage on the HMS Beagle supported his theories about the adaptation of species to their environments over time. His ideas challenged traditional views on creation and sparked significant debate within both scientific and religious communities, solidifying his legacy in the field of biology and transforming our understanding of life's diversity.