Leucippus and Democritus were important Greek philosophers from the antiquity. Leucippus was the first to have the idea of an atomic structure of all kinds of matter, 2500 years ago. Democritus was his disciple.
1. Democritus was not discovered the atom; he proposed and accepted intutively the notion of atom at approx. 400 bc. 2. Now the founder of atomism is considered Leucippus, precursor and teacher of Democritus.