An early figure in rhetoric, famous for the story where he learned to speak well by filling his mouth with stones and trying to speak past them.

Founded a philosophical system identifying pleasure as the supreme good and viewing the world as a random conglomeration of atoms, not ruled by any larger providence.

Epicureanism was one of two dominant philosophies during the late Roman Empire, alongside Stoicism, which was more popular. One difference was that most of the system was thought up by Epicurus himself, whereas Stoicism has had many authors contributing to its evolution.

The "first philosopher" (not really). Influenced other thinkers who went on to create the major schools of philosophy. For example, he taught Plato some things, who then taught Aristotle.

And Antisthenes took to himself Socrates' character more than his ideas, and taught the famous Diogenes the Cynic, who taught Crates, who taught Zeno of Citium, who created Stoic philosophy.

The inventor of decimal numbers, sort of.

Developed al-jabr, i.e. algebra. Studied Indian numerals, and his works were translated into Latin in the 12th century, which introduced the West to decimal notation.