1. Sapiens by Yuval Noah Harari
2. Einstein: His Life and Universe by Walter Isaacson - What was interesting for me to learn was that even though he was a great scientist, he was very humane in other aspects - and you can easily relate to.
3. The Hitchhiker's Guide to the Galaxy by Douglas Adams - Fun read which is also deeply philosophical at the same time. Got me interested in science fictions as a genre.
4. Meditations by Marcus Aurelius - Great intro to stoic philosophy