Monster is magnificent. It’s a psychological thriller set in pre-unification Germany that tells the story of how a talented Japanese neurosurgeon deals with the repercussions of saving one human life over another. It’s a study of morality, human nature, and the origin of evil.
The anime is a bit dated now, but still holds up. Planning to rewatch it soon!
One Piece, Monster and of course HxH have all impacted me.
For books, most people have already mentioned Dune, HHGTTG and The Culture series, so I'll have to add Flowers for Algernon.