Claudius Ptolemy was a major astronomer and geographer from the Library at Alexandria.
The philosopher Panaetius is called the founder of Roman stoicism.
When Aristotle described the Pythagoreans, he referred to the writing of the Pythagorean philosopher Philolaus.
Porphyry was a 3rd century A.D. neoplatonist.
Protagoras was the earliest known sophist who taught for pay.