Asklemmy

I hesitate to call her a great author in her own right and I detest her attitude towards transwomen. That said, J.K. Rowling's Harry Potter series transformed the young adult fiction genre from a bit of a wasteland of Nancy Drew and Hardy Boy novels into a quality genre with significant cross-generational appeal.

I'll mention Orson Scott Card as well, but his books have worn thin over time as he squeezes every penny out of the Enderverse. Ender's Game got me through a miserable hospital stay as a young child, so it will always have a special place in my heart. Speaker for the Dead I also loved.

I just thought of another: Bernard Cornwell. His novel series (Sharpe, The Last Kingdom, etc) are phenomenal historical fiction.

Philip Pullman of his dark materials fame?

So many good answers already that I agree with. So I'll add James Ellroy and Clive Barker

For Ellroy, the entire LA Quartet remains a pivotal sea change in "hard boiled" crime fiction; taking a lot of the conventions created by the likes of Hammett and Chandler and updating them for a modern audience.

Barker is a more personal choice. But his writing is just so evocative and descriptive that I couldn't NOT mention him. Imajica literally changed my literary life, with Weaveworld being (in my opinion) a less dense, more reader friendly version of Imajica.

Margaret Atwood

Ted Chiang

Greg Egan

Peter Watts

Adrian Tchaikovsky

Gene Wolfe - the style of his sci-fi is mesmerizingly mysterious, even the mundane things described take on sinister tones

Roberto Bolaño

Cixin Liu. Not only is the Remembrance of Earth's Past trilogy (Three Body Problem) epic, his short stories are really fun reads.

Guy Gavriel Kay. First book published in 1984, part of a trilogy that was Tolkien-esque, quite decent, but not exactly ground-breaking. He's since gone on to something a little more unique, which he describes as "historical fiction with a quarter-turn to the fantastic." Impeccably researched but set an alternate world that's a close but not exact mirror of our own. This allows him to take a few small liberties with historical accuracy in service of telling a better story. Personally I think he really hit his stride in 1995 with The Lions of Al-Rassan, and almost everything he's written since then has been exceptional.

Elmore Leonard. Dude was a massive influence on popular culture. He was instrumental in teaching Tarantino how to be Tarantino. He wrote the books that SO MANY great movies and television shows were based on.

Hunter Thompson. His gonzo style is often imitated but rarely duplicated. And it's such a goddamn simple concept, but no one else managed to do it with his flair.

Tom Robbins and Tim O'Brien

aside from some of the more obvious choices (rushdie, wallace, mccarthy, morrison):

don delillo, esp. underworld and white noise

ted chiang, esp. exhalation

marilyn robinson, esp. housekeeping

denis johnson, esp. jesus' son and tree of smoke

colson whitehead, esp. the intuitionist and the nickel boys

and while relatively new so maybe not at the same status as some other writers, jamil jan kochai and nana kwame adjei-brenyah will be making lists like these in the future if they keep writing the way they have.

IMO Charles Stross should be up there with the masters with his Laundry Files.

From Wikipedia:

The Laundry Files is a series of novels by British writer Charles Stross. They mix the genres of Lovecraftian horror, spy thriller, science fiction, and workplace humour.

Octavia Butler and her likely prophetic Sower series on how US descent is gonna occur

Henning Mankell for a bit of Scandi crime

And I don’t see anyone mentioning Doug Adams !?

Iain (M) Banks

China Mieville

Two of my faves

Gabriel Garcia Marquez started before 1970 but his career stretched long after.

Walter Moers is a German writer best known for creating 'Captain Bluebear' in my all time favorite book. He has since written several fantastic novels based on the continent Zamonia. In some ways I think you could compare bis work and way of writing to Terry Pratchett's.

https://en.m.wikipedia.org/wiki/Walter_Moers

Another German author that gave me lots of great hours of reading growing up is Cornelia Funke. For me it was mainly the book Dragonrider, but she is also well known for her Inkheart series and The Thief Lord.

https://de.m.wikipedia.org/wiki/Cornelia_Funke

Tamsyn Muir will almost certainly be remembered extremely positively. She’s only got a few books out so far, but they have such a distinctive voice and style that’s hard to compare to anyone but Shakespeare.

Idk if she holds up outside English though, everything else is great, but the way she plays with words is part of her appeal.

I always enjoyed reading Michael Crichton. He might not have been the greatest novelist, but I liked his ideas and always learned a ton reading his books.

N. K. Jemison

Thomas Pynchon.

Iain M. Banks Terry Pratchett

To me, it has to be Steven Erikson. Malazan series is simply amazing.

Stephen King.

King of Horror.

He has written hundreds if not thousands of stories over the last half century. So many of those have turned into Blockbuster movie, lame TV movies, Indie films, and TV shows. We can argue later about how "literary" many of those stories are, but his impact on popular culture today is undeniable.

Although he has occasionally written or said some cringey things out of touch with the current zeitgeist (who hasn't?) and has struggled with his own demons, from what I've seen he has always demonstrated that at his core he's a decent human being struggling, like we all do, in a scary world.