A Greek philosopher/scientist, who lived from approximately 450 BC to 420 BC. Very little is known about him on a personal level (this is not lazy noding on my part: I can find practically no reliable evidence that the man even lived anywhere). The first of the atomist school, Leucippus has been rather unfairly overshadowed by Democritus, who became well known for many of the ideas that Leucippus had proposed. Epicurus would also make liberal use of many of his ideas. However, even Leucippus' thinking is based on earlier Greek science and metaphysics. He adopted Parmenides' conception of fundamental elemental particles, as well as Heraclitus' principle of endless movement. From this, he developed the theory that matter is made up of a multitudue of miniscule particles. He believed these to be the smallest of all possible objects: they could no be divided or reduced. All scientific phenomena could be explained by the movement of these atoms. Fast forward to the 1800's, and John Dalton is finding out that many of Leucippus' theories were, at least, very well educated guesses. A smart guy.