If you know what Welcome to the NHK even is(for the record I did not) I wouldn't be surprised if your ubiquitous MC is really just yourself. Write what you know, I guess!
I always felt that Dick Francis wrote about essentially the same man over and over. And it was certainly profitable for him. But he was still able to write about different characters. If I look at the Sid Halley novels, for example (the most useful for me because they repeat the same character), Halley's ex-father-in-law is a very different person, as is his kinda-business-partner Chico Barnes. Which leads to my suggestion: Write about your "repeater" character. Give him important close people in his life. Write about those people until their personalities are cemented and it's too late to rewrite them with the repeater's personality. And then make one of *them* a main character. My guess, and it's purely a guess, is that the character is shaped by the writer's intolerances in personality characteristics. I don't mean that they're creating a perfect character, but that there are probably a small set of positive personality characteristics that they just can't stomach their character not having, and a small set of negative personality characteristics that they can't stomach their character having. Complying with those preferences once can still produce a perfectly good character, but if you keep complying with them, you're going to keep creating characters with a similar flavor.
Brilliant insight! Enough exposure to great literature will make you realize some of the best characters have cringeworthy characteristics.
With the latter, ironically enough, I now realize its because I can't picture an MC without certain flaws. (in this case, complete failure to have social ability, and failings in certain academic areas.) Hence, by always have certain flaws, it ends up biasing the character to certain concepts. But yeah, the former suggestion is probably my way out, and is the closest I've come to that.
When I was just starting out writing seriously, in my late twenties, I had about three stories on the go that all featured pretty much the same character: an older guy, maybe sixty or so, whose life hasn't gone the way he wanted it to, and who wants to recapture his youth in some way. The stories were all very different - one was a medieval fantasy, one a realistic modern-day story, and the third a science fiction piece, but they all featured an MC like that. Looking back, it seems strange that a guy in his twenties would be writing that kind of character so obsessively, but it happened. I have abandoned two of those stories, and the other (the medieval fantasy) is still on the back burner. First draft complete at 78,000 words, second draft should be about 100,000 words. Once I saw that I was repeating myself, I stopped doing that. I didn't deliberately force myself to avoid that character; it just happened. It seemed that just my being aware of the issue made me cast my net a little wider. The stories I'm writing now have a variety of very different characters, and I couldn't be happier about it.
Motives are a big factor in differentiating characters. It determines how and why they think, act and react they way they do. Three people raised in similar backgrounds, in the same field of work and even working in close proximity can be potrayed dynamically from one another with different motivations in the plot. A bonus to clearly establishing their motive is your dont have to release too much information about their past if that conflicts with your overall plot.
Yeah, I think that's what I'd do. In fact it IS what I do. Pick a person you 'know' and write them as a character. (Obviously disguising them heavily...) I've even pushed myself by making a female character of mine think and behave a lot like a male friend of mine...without making her the least bit masculine. But it's little things like how they express themselves, what would they think or do in certain situations, etc. This is really a starting not a finishing point. You can, of course, alter the character to suit your story. But it's a good way to challenge yourself when writing a character, and will make you do things with that character you might not have done, if you'd started from 'scratch' to construct your character out of thin air.
I actually didn't notice until someone pointed it out to me one time by saying "I like how most of your characters are dark melancholic killers" I was like wait what? I think it's got something to do with the fact that the first character I ever made (about eight years ago or so) had these characteristics so I suppose all my other characters just started to resemble him. Starting to pull myself away from that one characteristic because it wasn't even just my main characters that all had the same character. Almost entire stories were filled with almost replica's of the main character. Luckily I've made the first leap with my antagonist who's definitely a lot more outspoken even though he'd been in the business of killing a lot longer than my antagonist he'd taken it a different way. So instead of holding in his thoughts or thinking carefully before acting; he'll shout em to the world and act on impulse. And instead of being depressed over the people he's killed; he often kills people because they annoyed him and enjoys torturing wealthy people just to see them on their knees begging for their lives (A messed up childhood and having the power to be exempt from the law does that to a guy).
