Yes, yes he was.
He was student of the philosopher Leukippos.
They created the original atomic theory. They created the idea that the atom exists and that it is indivisible.
They helped form the roots for the first major philosophies. They explained that everything arises mechanically out of a coalescence of an infinite number of irreducible atoms. Leucippus said,...
Coining of the term "atom" and the idea that matter was composed of small, invisible, indivisible particles.