Original: Leucippus or Leukippos ( Greek : , first half of 5th century BC ) was the first Greek to develop the theory of atomism -- the idea that everything is composed entirely of various imperishable , indivisible elements called atoms -- which was elaborated in far greater detail by his pupil and successor , Democritus .
Simplified: Leucippus or Leukippos ( Greek : , first half of 5th century BC ) was among the earliest philosophers of atomism , the idea that everything is made up of many imperishable , indivisible elements called atoms .