Charles Darwin is the scientist known for his work on the theory of evolution. His seminal work, "On the Origin of Species," published in 1859, introduced the concept of natural selection, which explains how species evolve over time through the processes of variation and competition for resources. Darwin's observations during his voyage on the HMS Beagle, particularly in the Galápagos Islands, were crucial to formulating his ideas. His work laid the foundation for modern evolutionary biology, significantly changing our understanding of life on Earth and its complex interconnectedness.