I've mostly focused on authors who have relatively recent careers, but I wanted to at least mention the reading possibilities for older writers you may have missed.
If you somehow haven't read Tolkien, remedy that.
Read The Worm Ouroboros as a good parallel to Tolkien and consider how what we consider standards of the fantasy genre are just one take on an older formula.
Ursula le Guin
Her books are frequently shelved with children's books only because they don't have high sex and violence content. This is thoughtful fantasy that takes a turn for the philosophical at times and comes from a distinctly non-dualistic worldview. If you haven't read her work as an adult, definitely consider it.
Though he wrote more than fantasy, his Phantastes is interesting for fans of the genre. It is like a transitional form between fairy tales and modern fantasy.
One of the forerunners of modern fantasy. George RR Martin cites him as an influence and you can see the similarities in the mixed whimsy and brutality of the Lyonesse trilogy. His Cugel trilogy also brought antiheroes to fantasy and was a major source for Dungeons & Dragons.
He wrote fiction of many types, always requiring thought to interpret. If this is to your taste, definitely read his fantasy.