Don’t recall if the following is one of Elmore Leonard’s writing rules, but he has admonished that even if it’s just a gunsel used in one passage, do your best to give that hood some sort of individuality, some sort of dimensionality. Keeping that in mind, when I introduce a character who is frankly fulfilling a plot function, I often imagine a physical, psychological or back story attribute to that character. None of this may make it onto the page, but it will shape how I describe my other characters reacting to this character or how this character speaks.
What also intrigues me, and writers from the aforementioned Mr. Leonard, Jules Verne to Asimov and James Ellroy, will have a seemingly secondary or minor character show up in one story yet take center stage in another. To me that’s like in comics where we now have the DC Universe – or DC Universe 2.0 as they did a reboot of all their characters a year ago, the New 52 (as in 52 titles) – and now, well, Marvel Now. The latter comes in the wake of the reverberations of the Marvel Universe-wide X-men versus Avengers and is billed as a re-launch, not a reconfiguring of its characters like DC did.
Not to worry, this is not the forum where I’ll get all fanboy, geeked out on inconsistencies in timelines here; like how does a now younger New 52 Batman/Bruce Wayne have an 18 or 20-year-old Dick Grayson (former Robin, boy wonder sidekick, now Nightwing, a costumed vigilante in his own right) as his ward? To return to the point, it’s kind of a cool thing to build your own world, working out the interconnections. I’ve done it where I’ve had a main character referenced, sometimes obliquely, in another book or short story. There’s a mega-conglomerate I’ve used, a many headed company called SubbaKhan or its subsidiaries have shown up in several of my books with diverse storylines.
I hope one day to employ even a small percentage of the myriad characters and institutions Marvel and DC, Verne and Asimov, have introduced and cross-pollinated in their stories. To have some characters who are secondary or tertiary in one setting, step from the shadows and take center stage in the next and go back to having a cameo if you will in another setting. Some die, some change, some move on and some are reimagied – like say extrapolating what ever happened to Wilmer (thus the still of the great character actor Elisha Cook Jr. who played Wilmer in the Maltese Falcon film) after he got out of prison.
For me then, being interested in my major and minor characters helps me to keep them interesting.