Thomas is also known for his championing of Golden Age comic-book heroes – particularly the 1940s superhero team the Justice Society of America – and for lengthy writing stints on Marvel's X-Men and The Avengers, and DC Comics' All-Star Squadron, among other titles.

[9] Enthusiasm for the rebirth of superhero comics during that period led Jerry Bails to found the fanzine Alter Ego, and Thomas, then a high school English teacher, took over as editor in 1964.

In 1965, Thomas moved to New York City to take a job at DC Comics as assistant to Mort Weisinger, then the editor of the Superman titles.

This came after his chafing under the notoriously difficult Weisinger, to a point, Thomas said in 1981, that he would go "home to my dingy little room at, coincidentally, the George Washington Hotel in Manhattan, during that second week, and actually feeling tears well into my eyes, at the ripe old age of 24.

"[11] Familiar with editor and chief writer Stan Lee's Marvel work, and feeling them "the most vital comics around",[11] Thomas "just sat down one night at the hotel and – I wrote him a letter!

[13] The writer's test, Thomas said in 1998, "was four Jack Kirby pages from Fantastic Four Annual #2 ... [Stan Lee] had Sol [Brodsky] or someone take out the dialogue.

[15]To that point, editor-in-chief Lee had been the main writer of Marvel publications, with his brother, Larry Lieber, often picking up the slack plotting of Lee-scripted stories.

Two previously written freelance stories for Charlton Comics also saw print: "The Second Trojan War" in Son of Vulcan #50 (Jan. 1966) and "The Eye of Horus" in Blue Beetle #54 (March 1966).

That notable run was marked by a strong sense of continuity, and stories that ranged from the personal to the cosmic – the latter most prominently with the "Kree-Skrull War" in issues #89–97 (June 1971 – March 1972).

When that title became the solo comic Doctor Strange, he wrote the entire run of new stories, from #169–183 (June 1968 – Nov. 1969), mostly with the art team of penciler Gene Colan and inker Tom Palmer.

[19] As Thomas self-evaluated in a 1981 interview, shortly after leaving Marvel for rival DC Comics, "One of the reasons Stan liked my writing ... was that after a few issues he felt he could trust me enough that he virtually never again read anything I wrote – well, at least not more than a page or two in a row, just to keep me honest.

"[21] Thomas eloped in July 1968 to marry his first wife, Jean Maxey,[22] returning to work a day late from a weekend comic-book convention in St. Louis, Missouri.

[25] While efforts to save it failed – the title ended its initial run with #66 – Thomas' collaboration with artist Neal Adams through #63 (Dec. 1969)[26] is regarded as a Silver Age creative highlight.

[28] Thomas and artist Barry Smith launched Conan the Barbarian in October 1970,[29] based on Robert E. Howard's 1930s pulp-fiction sword-and-sorcery character.

The series contained the usual elements of action and fantasy, to be sure, but it was set in a past that had no relation to the Marvel Universe, and it featured a hero who possessed no magical powers, little humor and comparatively few moral principles.

[35] Thomas, with Marvel writers and artists, co-created many other characters, among them Ultron (including the fictional metal adamantium),[36][37] Carol Danvers,[38] Morbius the Living Vampire,[34] Luke Cage,[39] Iron Fist,[40] Ghost Rider,[41] Doc Samson, Valkyrie, Werewolf by Night,[42] Banshee and Killraven.

[52] In 1975, Thomas wrote the first joint publishing venture between Marvel and DC Comics – a 72-page Wizard of Oz movie adaptation in an oversized "Treasury Edition" format with art by John Buscema.

[19][64][65] Conway also contributed ideas to the talking animal comic Captain Carrot and His Amazing Zoo Crew!, created by Thomas and Scott Shaw.

[68] During that era, Roy Thomas and Gerry Conway collaborated on the screenplays for two movies: the animated feature Fire and Ice (1983) and Conan the Destroyer (1984).

[70] As a solo writer, Roy Thomas wrote Wonder Woman and, with artist Gene Colan, updated the character's costume and introduced a new supervillainess, the Silver Swan.

Reviving the Golden Age group in Justice League of America #193 and continuing in All-Star Squadron,[72] he wrote retro adventures, like those of The Invaders, set in World War II.

In addition to the JSA's high-profile heroes, Thomas revived such characters as Liberty Belle, Johnny Quick, Robotman, Firebrand, the Tarantula, and Neptune Perkins.

A one-shot issue titled The Last Days of the Justice Society involved most of the JSA battling the forces of evil while merged with the Norse gods in an ever-repeating Ragnarok-like Limbo was written by Thomas, with art by David Ross.

He scripted titles starring Doctor Strange, Thor, the Avengers West Coast, and Conan, often co-scripting with Dann Thomas or Jean-Marc Lofficier.

For a series of independent publishers, he wrote issues of the TV-series tie-ins Xena: Warrior Princess, Hercules: The Legendary Journeys and The X-Files for Topps Comics.

In 2012, Thomas teamed with artists Mike Hawthorne and Dan Panosian on Dark Horse's Conan: The Road of Kings, which lasted 12 issues.

[88] Thomas had a cameo appearance as a prison inmate on the third season of Marvel's Daredevil, released in October 2018 on Netflix, and wrote a blog entry about this experience.

In a guest column in The Hollywood Reporter, Thomas took issue with Riesman's assessment of conflicting accounts of the work of Lee and Jack Kirby, who is credited with co-creating many classic Marvel characters.

However, the remaining (and crucial) 5 percent of its content, scattered amid all that painstaking research and well-written prose, renders it often untrustworthy...i.e., a very bad biography.

Thomas's two-part story takes place right after The Incredible Hulk #181 and right before Giant-Size X-Men #1 and reveals a missing link mystery about Wolverine's costume.