Marble bust of Democritus, circa 1700-1750; Victoria & Albert Museum, London, UK
wiki: Democritus was a student of Leucippus and co-originator of the belief that all matter is made up of various imperishable, indivisible elements which he called "atomos", from which we get the English word atom. It is virtually impossible to tell which of these ideas were unique to Democritus and which are attributable to Leucippus.
According to legend, Democritus was supposed to be mad because he laughed at everything, and so he was sent to Hippocrates to be cured. Hippocrates pointed out that he was not mad, but, instead, had a happy disposition. That is why Democritus is sometimes called the laughing philosopher.