I had the same question and came across a book called "Sophie's World" which tells the story of philosophy in human history, starting with Socrates and coming all the way to modern times. https://en.wikipedia.org/wiki/Sophie%27s_World

I'm currently about half way through, i think the book is geared towards a younger audience but i'm finding it really enjoyable.

Once you have a high level view of the highlights of philosophy, you can answer for yourself which philosophers to deep dive on.