Democritus was an ancient Greek philosopher who lived around 460-370 BCE. He is best known for his early ideas about the nature of matter, proposing that everything in the universe is made up of tiny, indivisible particles called atoms. This concept was revolutionary, as it suggested that matter is not continuous but rather composed of distinct units. His ideas laid the groundwork for modern science, influencing later thinkers like John Dalton and the development of atomic theory. Although Democritus's theories were not widely accepted in his time, his work has had a lasting impact on our understanding of the physical world and the nature of existence.