Red shirts, on the other hand, were The Expendables long before Sly Stallone coined the name for his films.
As writers, we have to guard against creating our own Expendables. Okay, in some stories, like thrillers, or murder mysteries, someone has to die. Already, this character is an expendable...he or she is redundant.
Or are they?
The best example I can think of an Expendable (note, NOT redundant) is in this book, the superlative 'Rebecca' by Daphne du Maurier
How many stories do you know of that have already killed off their main character? Or if you do, how many do it as well as 'Rebecca'?
One of my other favourite authors, Stephen King, can either write tonnes of expendable (and sorry to say, forgettable) characters like in Needful Things, or can focus on just a handful, and do it brilliantly, as in Misery.
Any which way we cut it....if you are a reader and are then told 'and then Mikey died...' you might feel cheated. After all, did we care about Mikey enough to have some feeling about his death? No? Then the writer did not build his story up enough.
If we knew that Mikey had been orphaned because his parents had been murdered, if we knew that he had been put into social care because he had no other family....if we knew he had found love, lost it, and found it again (or that the love of his life actually killed him)...we would care, wouldn't we?
But some characters get a line or two of introduction in an 800 page story, and before you can say 'man....you have to GO'...they're gone. Have you read books like that? How did you feel when you read that? If it was 'okay, I forgot who Mikey was because he hasn't been mentioned since page 142', then I think the author has overlooked a very important thing.
Sometimes, we read a book and watch a film just for the ride....I'm talking 007, Rocky, any Doctor Who episode. Will anything fatal befall the main characters? Really? Unlikely. So where's the drama? If no-one is at risk - no-one that we care about...no-one that we care about that the author has created, then basically, all you can do is enjoy the ride.
But creating swathes of expendable characters is not good. It is not good 'filler' for a story.
You can create a sword wielding goon, for instance, if it is possible he or she can kill the main character. In Raiders of the Lost Ark, there was originally a long fight scene between Indy and the sword guy. But the final script was that Indy just shoots him! Is it funny? In this context, sure....but do you recall the character? We remember him, because of his part in the movie. We don't need to know his name or anything else. In a film like this, it is a good use of an Expendable. As writers, we are not afforded the same luxury, and our Expendables have to be better drawn.
We cannot simply introduce someone, give them a name, describe their looks and their basic motivations in a paragraph, only to drop them off the radar, only to bring them back near the end of the book to create some drama. And then, they realise that they were an expendable character.
I got the same reaction from someone who watched Harry Potter and the Goblet of Fire, but who hadn't read the book.
"Why does Cedric die?" he said.
"So he can turn up in the next Twilight film, I suppose," was my reply.
His point was (even though others watching the film had read the book) that to a viewer, Ced was an expendable....he is hardly in the film version of GoF (by far the worst HP film I believe).
WOOP! WOOP! SPOILER ALERT!!!
Mike Newell may as well have gone and put Cedric in a red shirt, for all the screen time he got. I know he dies in the book, but the film took the assumption that everyone had read the book.
So, one of things I try my hardest to do is create characters that readers will have some feeling about. If you don't care about the main characters, you will care even less about the supporting cast. Going back to Star Trek, and specifically, to Deep Space Nine, one of the strengths of that show was an amazing array of supporting characters, who would turn up every other episode.
Hate the show if you must...but what can't be denied is that it had great characterisation, and (save for two characters which I genuinely hated!) these characters gave a sometimes lightweight script, increased gravitas.
So unless your Expendable is 'Thug Number Two,' remember that all your characters must be relevant.
Happy reading and writing!