Epictetus was a Greek Stoic philosopher born as a slave.
One of his primary works was The Enchiridion which is available in various forms including a public domain translation at Project Gutenberg. It is a quite accessible beginning to learning about Stoicism. It was the first Stoic text I read after Ryan Holiday’s book, The Obstacle is The Way.
One of the key parts of Stoicism is to keep the ephemeral nature of our mortal being in mind, i.e. everyone will die. The purpose of this is not to be morbid or sad, but to keep in mind the proper priorities in life and not get caught up in petty things, especially those outside our direct control.
“Let death and exile, and all other things which appear terrible, be daily before your eyes, but death chiefly; and you will never entertain an abject thought, nor too eagerly covet anything.” - Epictetus, The Enchiridion
Like other great Stoic philosophers, Epictetus sought to live his philosophy rather than just speak it. He started as a slave, was crippled during a beating by his master which left him lame in one leg his entire life, and once gaining his freedom he started a school of philosophy. His writings were captured primarily by his students, especially Arrian, rather than by his own writing. Besides the Enchiridion the other primary work of Epictetus captured by Arrian is The Discourses.
A great modern translation of The Enchiridion along with excerpts from The Discourses is How to Be Free available on Amazon as both a small hardback and Kindle ebook.
Epictetus is my favorite of the Stoics to read because of the succinct, direct style of his teachings in contrast to the rambling style of Senaca the Younger. I also find it more clear than the writing of Marcus Aurelius in his Meditations, though to be fair he was writing a journal to himself.