[SuperScrounge]

Clumsy title aside this is for writers who had published work before they went to work for comics, or started in comics and later became published outside comics.

This seems to have become more common in recent years, as comics seem to be more highly regarded than they were in the Golden Age.

Eando Binder/Otto Binder - While there were some comic credits for Eando on some comic text stories, I'm not sure if Earl Binder (the E in Eando) had anything to do with these stories or it was just Otto (the O in Eando) using the old shared pen name. Otto, of course, was famous for writing the most Captain Marvel stories (537), his house was called The House That Captain Marvel Built & Otto admitted he got paid enough to pay for the house twice over.

Edmond Hamilton - The world saver himself did work for DC Comics (he was asked by friend Julius Schwartz) writing science fiction comics, Batman, Superman and Legion of Super-Heroes stories.

Henry Kuttner - I believe he'd been published before writing comic book scripts for the original Green Lantern. He tended to write a number of humor stories featuring GL's sidekick, Doiby Dickles, because his wife, writer C. L. Moore, loved those.

Alfred Bester - Got his start working on Green Lantern when Kuttner was the primary GL writer. When Kuttner retired and Bester became the main GL writer he sidelined Doiby Dickles as he couldn't stand him. Oddly his favorite work in comics was the humorous The Answer Man stories.

Mickey Spillane - Got his start in comics writing text stories and comic scripts. His famous detective Mike Hammer was based on a character he created for a comic series that got scrapped (although the original script was later turned into a comic.)

Patricia Highsmith - Got her start writing the Black Terror for Pines/Standard/Better and the Blonde Phantom for Timely/Marvel before turning to novels.

Ray Cummings - Started off doing science fiction, then wrote some Captain America stories for Timely/Marvel, including an adaptation of his story The Girl In The Golden Atom.

Harry Harrison - I'm kind of amused by the fact that he was later famous for his science fiction novels, he got his start as a comic book... artist. Yeah, maybe he wrote some of the stories he drew, but usually it's his comic book art I hear of, not his comic book writing.

That's all I can think of at the moment.Who do you know of?

[Robb_K]

Ray Bradbury had some of his stories published in comic books.  He had some Sci-Fi stories published in magazines before any were printed in comic books.  He later had not just pulp Sci-Fi paperbacks published, but also hardbound books.

I'm sure there were several other famous Sci-Fi writers who had some stories printed in comic books, in addition to magazines, pulp softcover books, and standard hardcover books.  I don't know who they are, other than the early (1930s and early '40s) comic strip writer/artists, because I didn't read Science Fiction comic books.

[Electricmastro]

Not sure how well-known George Mandel is in general, but he worked in multiple mediums regardless:

[mopee167]

There's also Gardner F. Fox. Most of his 100+ novels were published after he left comics, but he did write a few short stories for the pulps in the 1940s, including Weird Tales.

[Electricmastro]

Leonard Starr had written for the Thundercats show in the 1980s:

https://thundercats.fandom.com/wiki/Leonard_Starr

Though I had actually first consciously taken notice of him for his Liquid X work for Lucky Comics #1 (January, 1944):

[paw broon]

In recent years 2 Scottish novelists have written graphic novels: Ian Rankin and Val McDermid.  George Mann does both  but I don't know which discipline came first.

[SuperScrounge]

Yeah, it seems like going back and forth between comic stories and prose stories is more common these days.

Steve Englehart and John Byrne have written prose novels. (Byrne's novel actually ties into one of his comic series.)

Don Glut has non-fiction books about dinosaurs.

R. L. Stine wrote a Man-Thing mini-series.

Stephen King wrote some comic scripts (Creepshow, American Vampire).

[The Australian Panther]

Harlan Ellison wrote comics and also had some of this works adapted to comics. Stan Lee wrote his first novel