Simone de Beauvoir was an existential philosopher and feminist, perhaps best known today for her highly influential work, The Second Sex, sometimes said to be the start point for Second-wave Feminism. The Marquis de Sade was an 18th century revolutionary and philosopher, perhaps best known for his erotic work and scandalous sexual exploits.
Gottfried Leibniz was a German polymath, having major contributions to mathematics, philosophy and science. He also wore super huge wigs all the time. Seriously, look him up on Google images. He didn't mess around with the wigs. Spinoza was a contemporary of Leibniz, and apparently they even met. Spinoza did not wear nearly as huge of wigs, however.
Hilary Putnam and Donald Davidson are both 20th century American Analytic philosophers. They both worked on a wide variety of areas, but the comic references two of their thought experiments concerning philosophy of mind. The Brain in a Vat and the Swampman.
Socrates was really annoying, and tried to get people to define the nature of justice at pretty much every party he went to, even though everyone else just wanted to drink and have a good time.