Charles Darwin was the scientist who developed the theory of evolution. His groundbreaking work, particularly outlined in his book "On the Origin of Species," published in 1859, introduced the concept of natural selection as the mechanism for evolution. Darwin’s observations during his voyage on the HMS Beagle, especially the diverse species he studied in the Galapagos Islands, led him to formulate his ideas about how species adapt and change over time. His theory revolutionized the field of biology, providing a scientific explanation for the diversity of life on Earth and influencing numerous fields, including genetics, ecology, and anthropology.