Epictetus

Was born into slavery in Phrygia, worked in Rome for a secretary of Nero, was lamed for life, and was eventually freed and exiled along with every other philosopher when Domitian expelled them.

He wrote nothing. The Discourses and the shorter Enchiridion were taken down by his student Arrian, which is the same route by which Socrates survives.

The core distinction is between what is up to us and what is not: judgement, desire and action belong to us, and body, reputation and property do not. He taught that freedom is available to a slave and unavailable to an emperor, and he had the standing to say it. Marcus Aurelius carried his notes.