Charles Darwin is known for developing the theory of evolution by natural selection. His seminal work, "On the Origin of Species," published in 1859, introduced the idea that species evolve over time through a process where individuals with advantageous traits are more likely to survive and reproduce. Darwin's theory was influenced by observations made during his voyage on the HMS Beagle, where he studied various species and their adaptations to different environments. His contributions greatly advanced the field of biology and changed the way we understand the development of life on Earth.