This is another one of those things that make me wonder where the OP is going with all of this. Does Gabrielle from Xena count? She certainly starts out with no skills, but over the course of the series she learns to fend for herself. Do skills gained in the field disqualify one?
I'm in the brainstorming phase of writing about him as an "extraordinary ordinary" in the line of Aunt May, Alfred the Butler, and Lois Lane, but different from them in that he's not the passive symbol of what needs to be protected and/or the helpmeet that helps the hero recover, but also is, at least, fray-adjacent. And it occurred to me in my beginner's level knowledge of heroic fiction that I wasn't aware of too many ordinaries that fight the good fight, you know, actively.
And the reason why it's important to me... well, it's a passive role to be the helpless person that needs protecting, the lover who's frequently the hostage, the guide who never steps into the fray.... And, no matter how beloved those characters are, how vital they are to the hero carrying on, they still lag in agency. There's something important about the Xanders and Gamgees of the world. Their ordinariness is their power, their strength. And they suggest to the reader that a commitment to do good and the capability to change the world is not limited to those with extraordinary gifts: the mutants, the sons of kings, the demigods...
Sam is a great example, better than Frodo as he doesn't get all the boons from the famous NPCs or the big honkin' magic item.
Jimmy Olsen is actually referenced in the series, so good one there.
Commissioner Gordon feels wrong, somehow, perhaps because he's important. He has a position and men at his command, although, granted Xander with season 8...
The assistants to Dr. Who are excellent examples, but isn't there the implication of a sexual relationship off screen? I only know the recent series, which had a wonderful episode with a former assistant, so...
Doesn't Rick Jones get combat gymnastics training from Captain America? (And there's some other stuff later on... psionics?) And, [off-topic] why didn't Giles train Xander and Willow and Cordelia in self-defense? Why does Cordelia have to wait for Angel to train her? Giles and Wesley spar with epee, for crying out loud! [/off-topic]
Odysseus had the aid of the gods at times, but he was certainly out of the class of Agamemnon and Achilles. Perhaps that swineherd that aids him when he gets back?
Madame Fatal is not a bad precedent, actually, although I'd love to know if she was doing this in conjunction with other heroes running around, which would make the connection closer.
I'm inclined towards Harker. The accountant vs. Dracula is a good line.
Ripley's possible, although I'd have never thought of her as ordinary.
The Lone Gunmen? Possible. Do they ever take the field?
And, yes, the 15th level commoner operating in a PC's world is pretty much the idea that I'm getting at.