Stoicism. The two major figures that I use to discuss stoicism are Viktor Frankl and Epictetus. Epictetus was born a slave and was crippled by his owner, but eventually was freed and found a happy life teaching Stoicism. Viktor Frankl wrote about finding meaning in life even living in the concentration camps. While not explicitly Stoic, his Logotherapy lines up very well with Stoic principles.
As an athiest I also like stoicism a lot. Epictetus is definitely a real one, loved reading discourses. Would also recommend Seneca although I found it a bit drier. And the famous Meditations from Marcus Aurelius.