Democratus, often spelled as Democritus, was an ancient Greek philosopher who lived around 460–370 BCE. He is best known for his atomic theory of the universe, proposing that everything is composed of small, indivisible particles called atoms. His ideas laid the groundwork for later scientific thought in the field of physics and chemistry, although they were not widely accepted during his time. In addition to his atomic theory, he also contributed to ethics and epistemology, emphasizing the importance of observation and reason.