Together, these two are probably the most quoted philosophers on the planet. Often said to be the founders of Western philosophy, they can be considered a dialectical pair—Plato was the idealist, with his abstract theory of forms (which introduced the concept of dualism into our culture), while Aristotle was the realist, with his emphasis on physical, empirical observation; Plato was the utopian elitist with his state run by purpose-bred philosopher kings, while Aristotle was the pragmatist, opting for a constitutional government run by a strong middle class. Between them, they laid the foundation for many subjects we still study today,  including ethics, politics, logic, rhetoric, metaphysics, and the sciences (although Aristotle did famously end up getting a load of things wrong).

They are portrayed in the book as a couple of naughty 12-year-olds. I first meet them trying to hoover the nadgers of a contingent of Greek philosophers in Tesco. They appear regularly throughout the narrative, always squabbling with each other, and usually followed by Socrates pulling his hair out and trying to keep them out of mischief.