Take Weird Tales for example. Leiber's most famous early horror story did not appear in "The Unique Magazine." "Smoke Ghost," which featured a spirit of evil created by a modern city, appeared in Unknown Worlds (October 1941) where John W Campbell pushed the definition of modern fantasy. Leiber wanted to write horror fiction using some of the same ideas as HP Lovecraft (though never in a slavish pastiche kind of way), taking the boogie men out of the haunted castles and European forests and bringing them to the streets of America. There was only one problem. Innovation courts rejection.
This was the simple economic truth of the pulp era. Fritz Leiber was not some wealthy heir, despite his father being the famous actor Fritz Leiber Sr. He needed the money the pulps provided. So do you innovate or imitate? This question drove Fritz to talk to other pulpsters. In Discovering Modern Horror Fiction II, Michael E Stamm explains:
The plot of "Spider Mansion" (Weird Tales, September 1942) is familiar to anyone who has seen The Rocky Horror Picture Show. A man and his mate end up in a creepy mansion, wanting to do nothing more than leave. The inhabitants of the house are weird and creepy. Secrets eventually unveil a terrible truth that the couple discover, then flee. The owner of the house is not Frankenfurter but Malcolm Orne, a famed midget who has mysteriously grown into a giant. With Orne is his beautiful wife, Cynthia, a figure right out of an Ann Radcliffe gothic novel.
The narrator and his wife Helen come to the house during a storm, eat a mysterious dinner during which Orne explains how his dead brother Martin had created a formula that controls size. Their host leaves the table to deal with his mastiff, though the sounds the listeners hear are those of shuffling and skittering. During the absence Cynthia gives the couple a secret message written on her hankie in lipstick. It says "Get out. For your lives."
This scenario contains so many gothic props that the reader suspects the author of a touch of parody. As Stamm puts it, it has "definite humorous overtones." Stamm also points out the story doesn't read like Leiber at all. John Pelan counters this in the introduction to The Black Gondolier and Other Stories (2001). "Spider Mansion" despite its gothic trappings is still a story of science gone wrong, a theme Leiber would use again.
I've tried to discover who the Old Hand is but haven't found any thing definite. Looking at the excellent stats in "Who Wrote the Most?" by Terence E. Hanley at Tellers of Weird Tales and thinking about the publication date, September 1942, this eliminates HP Lovecraft, Robert E Howard (who had died), and Clark Ashton Smith (who had retired and certainly wouldn't have made those suggestions anyway. He too struggled with innovation vs imitation.) In 1942, Henry Kuttner, Paul Ernst and Manly Wade Wellman had sold to WT but wouldn't be considered "old hands." Ray Bradbury, Allison V Harding, and Frank Owen all came after or started about the same time as Leiber.
The second most prolific writer was August Derleth (101 stories). He would have been more likely, also being a correspondent of HP Lovecraft. Derleth would publish Leiber's first book, Night's Black Agents in 1947. But Auggie wrote ghost stories like the classic "Mr. George" under his pseudonym, Stephen Grendon. The list of weird topics doesn't sound like his work. I think Derleth would have been more likely to direct Leiber towards Lovecraftian pastiche or English ghost stories in the MR James mode.
Edmond Hamilton, at number three, with 76 stories, is another good possibility. Hamilton's very first story at WT featured a giant invisible spider in "The Monster-God of Mamurth." Ed also wrote the most and best science fiction in the magazine, which would have appealed to Leiber. The advice doesn't sound like the ideas Hamilton would have promoted though. He didn't write gothic retread, but liked to explore sf and fantasy ideas. His "The Metal Giants" (December 1926) was one of the first killer robot stories. "He That Hath Wings" (July 1938) invented the idea of a mutant with wings (not Stan Lee). Hamilton was an innovator who found a home at Weird Tales, but even he would leave the pulps four years later to write Superman comics.
After Seabury Quinn, the most likely candidate for the Old Hand is Arthur J Burks at 29 stories. His score isn't that high, but Burks was one of the million-words-a-year men, writing for many different pulps. He bragged that he could generate a new plot from any ordinary household object. ("Oh no, the Egg Whisk of Doom!") The advice given Fritz sounds more like a recipe for the shudder pulps and Burks knew them well, having written a couple dozens tales for magazines like Horror Stories and Thrilling Mystery. The plot of an average shudder pulp story involved a supernatural-appearing situation that would be revealed at the end to be the work of a crazed dwarf.
No matter who the Old Hand was, Fritz Leiber only published eight stories with Weird Tales. After "Spider Mansion," Leiber wrote a few gems like "The Hound" (November 1942) in which he used Lovecraftian themes (along with the same title as a Lovecraft story), but in an urban setting. "The Dead Man" (November 1950) was the last of his WT stories. Editorial inflexibility at WT lost them one Leiber classic written in these years, the novel Conjure Wife (1943), setting the standard for modern urban horror. It appeared in John W Campbell's Unknown Worlds. Like with the sword-and-sorcery team of Fafhrd and Grey Mouser, Weird Tales had their chance, but passed on what would in retrospect be some of Leiber's best early work.
[UPDATE: GW Thomas solves the mystery of the Old Hand in the comments below.]
GW Thomas has appeared in over 400 different books, magazines and ezines including The Writer, Writer's Digest, Black October Magazine and Contact. His website is gwthomas.org. He is editor of Dark Worlds magazine.