Firaxis has been introducing Civilization 6's various world leaders for a good long while now; the latest is Pericles, who the developer has put in charge of Greece. Now, each country in Civ 6 gets a unique ability, and Greece's is Plato's Republic, which grants you an extra wildcard slot. Greece also gets a unique unit, the Hoplite, who receives a bonus when placed next to his Hoplitey chums. Finally, Pericles himself has a special ability, Surrounded by Glory, which provides culture bonuses depending on specific conditions.
There's a wee bit more in the following trailer. Civilization 6 is out on October 21.