This is a bit of a ramble, but:
I truly believe that Sir Terence David John Pratchett is the greatest fantasy author of the post-Tolkien era. No one has done it as well as he did - prose, characters, tone, plot, themes, humor - he was the master of all of them.
His words danced off the page, from single lines like Death’s
“LORD, WHAT CAN THE HARVEST HOPE FOR, IF NOT FOR THE CARE OF THE REAPER MAN?”
To the Vimes Boots Theory or Humans Need Fantasy monologues.
His characters are some of the most richly textured I’ve ever encountered - Death and Sam Vimes and Moist von Lipwig and Granny Weatherwax, each of them feels like they were given thought and care and used to tell stories that they were uniquely suited to tell.
He controlled tone like a master, from slapstick comedy to serious satire to tense moments where you feel that, just for a second, things might not be okay.
His plots were always believable in the context of the worlds he was telling, and were always engrossing - that the metaphysical adventures of Death and co. felt as natural a fit for Discworld as the starting of the setting’s first newspaper, the solving of street crime and unraveling conspiracies and the grand re-opening of a post office is proof enough of that.
He used these plots to explore themes of responsibility, social inequality and duty to a person’s community with razor-sharp wit and a deep anger for the injustice of the world around him. He fought the evils of the world with a pen and paper, even as he died. No one will ever do it like he did, but that he did it himself might just be good enough.
He brought comfort and joy and happiness and thought and introspection to millions.
GNU, Terry Pratchett. Mind how you go.