The Four Golden Boys (Funny, Don, Mental, Elmer)
"The Gold Ogre" was a totally weird Doc Savage novel where the main characters weren't Doc and the gang, but four scrappy mystery-solving teenagers clearly meant to be a "permanent" addition...who thankfully, we never heard from again.
Making Doc a guest-star in his own magazine who shows up midway through someone else's story, is exactly the kind of experiment you can do if you have a long lasting series, and one the series should have tried more, very much like that one novel written in the First Person.
The four mystery solving teenagers are basically the James Bond, Jr., Muppet Babies, or Tiny Toon Adventures versions of Doc and the Five, with brawny Don Worth as the Buster Bunny-like teen Doc Savage (Don, not Doc, get it?), "Funny" Tucker is the broadly drawn comic guy not unlike Monk in that he was both funny and fat, Mental, the erudite Johnny of the group who had the dignity and solemn gravitas of the original Doc that muscle boy Don Worth doesn't have, and Elmer Dexter, who had no clear 1:1 analogue in the five, but who had the five's sense of adventure, love of travel and dreamed of polar expeditions.
The four were placed in a mystery that involved murderous circus midgets, yet another Doc Savage mystery that involves killer circus freaks (see also: the Monsters). Basically, it's some high school lunkheads against the Murder Moppets from Venture Brothers.
As you might guess, the four new characters, added to an already crowded Doc Savage universe, were abandoned. They remind me of nobody quite so much as Captain Marvel's Lieutenant Marvels (Fat Marvel, Tall Marvel, and Hillbilly Marvel), a supposed "permanent addition" who lasted for one appearance and were utterly forgotten about afterward.
Side note: anybody who tells you the Super-Pets (except for Krypto), or the Lieutenant Marvels were a "major part" of their respective comics is flat out lying to you. Not honest error, but a deliberate misrepresentation, for the purpose of making these books sound sillier and more whimsical than they really were. (Ahem, Erik Larsen.) The Super-Pets barely showed up (and, other than Krypto, had exactly zero appearances after 1969). The Lieutenant Marvels only appeared once total in the entire Golden Age, and were only brought back in the 80s because superfan Roy Thomas remembered them.
The four amigos came about in a period in the Street & Smith hero pulps that saw the introduction of several new supporting cast members to once unshakably reliable, glacially unchanging mags. Heck, the cast of Grey's Anatomy changed more times in 7 years than either the Shadow OR Doc Savage did in the same time.
Notice that not a single one of the Four Golden Boys was a girl, though. Jeez, as if the world of Doc Savage wasn't a big enough sausage fest!
John Thunden from Fear Cay
Of all the supreme scrappers set up from the get-go as a physical match for Doc Savage (Bruze, aka the Sargasso Ogre comes to mind), John Thunden might be the most unlikely.
The source of his tremendous vigor? He devoted himself to regular exercise and to eating syliphium, a plant that, in the Roman world, was used to treat impotence. Thankfully, we were spared the image of a 137 year old man going to the bone zone. The story leads us to believe that Syliphium might be the source of eternal life, but as this is a Doc Savage story, in the end it turns out Syliphium is just a vitamin rich superfood that kept Dan Thunden vigorous into his old age, and is as much a source of eternal life as yogurt and spinach are.
Also, John Thunden has an attractive daughter (of course he does). Though you'd imagine the daughter of a 137 year old man would be 100+ years old, you'd be wrong.
As awesome as Thunden would be in a feature film, I somehow doubt they'll go in that direction.
Lea Aster is homely monkey-like chemist Monk's sexy secretary, taken prisoner back in "Land of Terror," and never mentioned ever again.
Monk brags about her as being a "honey," and a "real peach," which I'm guessing is Old Person for smokin'.
It's easy to imagine her leaving Monk's service after Land of Terror. Even if she didn't work for a horny monkeyman trying to play a game of grab-ass, she still is in danger of being attacked by ancient Mayans, archers dressed up in silver, trained panthers, and assorted Thousand-Headed Men.
Of all the characters on this list, I can see Lea Aster showing up in the movies more than the others (though the chances are still remote), simply because she gives the single most interesting of Doc's allies an inner life and a supporting cast independent of being Doc's buddy.
Interestingly, Monk isn't the only hero to have a secretary who gets involved in the action. That would also include the sinister Atlantis-seeking Doc Savage clone Sun Koh, published in Nazi Germany. One of his allies was a badass old lady who had children who died in the Great War, and who kept a loaded machine gun under her desk.
You know, I have to get around to reviewing Land of Terror, because it was full of many attempts to give the aides inner personal lives independent of their work with Doc. The best example would be electronic expert Long Tom's tricked out supercar, which had an electrical antibug field several years before "bug zappers" became widespread. Long Tom always seemed like an interesting guy who was relegated to the background, much like many Star Wars characters who got an action figure: in "The Phantom City," we hear he had a personal museum of electronic gadgets taken from numerous battles.