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[Linked Image from betweenthepagesblog.com]

From JIMMY OLSEN 147, with the character "Angry Charlie", one of the creatures genetically bred in the Evil Factory in previous issues,. he Evil Factory was blown up and destroyed in JO 146, but Angry Charlie and other creatures from it survived. Jimmy Olsen was recovering in a hospital room in the opening scene when Angry Charlie burst into the room. In the last few issues this wild bug-eyed monster met and made friends with the Newsboy Legion, and they more or less adopted him as a pet and at times fighting ally. Or as in this scene, a random threat that provides action in the scene.
https://onemillioncomics.com/supermans-pal-jimmy-olsen-v1-147/

Like so many other characters introduced, in the explosion of new characters Kirby created in JIMMY OLSEN, Angry Charlie was given limited space due to how many other characters were already in the series. But in the limited space he was given, interesting, and plenty of potential for expansion, maybe even into another series.
Along with The Wild Area, the Hairies, the Zoomway, the DNA Project, the new Newsboy Legion, the new Guardian, Dubbilex, a giant green renegade Jimmy Olsen clone, thousands more tiny Jimmy Olsen clones and Newsboy Legion clones, The Evil Factory, Dabney Donovan and his many research projects, the planet Transilvane, monsters around Loch Ness on the loose either created to protect the nearby Evil Factory, or just got loose from it, the seemingly endless range of mutant creatures shown in the Evil Factory's zoo in issues 145 and 146, and even after blowing up the evil factory, thousands of these could be used in future stories as having survived the explosion that destroyed it, as Jimmy Olsen survived. And in the last two issues, Angry Charlie and (patterned in a Jules Verne template) Victor Volcanum and all HIS gadgets and creations, expose yet another vast secret hidden world.

That's all just one 15-issue Kirby series, and not even a complete list of characters and worlds introduced !

Over at Marvel, a similar set of throwaway characters were expanded on and became the core of the Marvel Universe: the Inhumans,their city of Attilan, the Blue Area of the moon, the Watcher and his race, Galactus, the Silver Surfer, the Mad Thinker and his androids, "Him"/Warlock, Dr. Doom and his Latveria kingdom, the Microverse, Black Panther and Wakanda, the Sentry and the Kree empire, the Skrulls, Sub-Mariner and Atlantis, and that's just a small tip of the iceberg.

Like Angry Charlie, just a sample of the torrent of new characters and hidden worlds exploding out of any Kirby series.