May he rest in peace.
Zen and the art of motorcycle maintenance was one of the first books on philosophy that I read outside of my philosophy curriculum at university and it stayed with me.
It's a great book discussing the metaphysics of quality, but not just that. It's written in a captivating way, mixing both the 'food for thought' as well as a pleasant narative about a father and a son on a motorcycle trip.
It's one of the philosophy books that I can recommend to people who are not directly interested in philosophy as well, which gave me some quite fun discussions with my friends about the topics in the book without being too deep into the philosophy itself.