Article: "Writing Secondary Characters That Pop—And Sell More Books"

[Quantum]

If you are writing a series, secondary characters are critical to its success. That’s a big statement, but I’m going to try and back it up.

Secondary characters have always been important in books. Authors use these characters to broaden the seams of the story and add depth with layers of conflict, drama, or humor.
..
I wrote about a nerdy aerospace engineer whose older brother, Connor, taught him all the wrong things about women. He was awful and chauvinistic. Connor was the antihero of any romance book. Even my editor sighed when she read the book, and told me Connor would never have his own story.

That was okay, because I had no intention to continue his tale.

Until my readers began e-mailing me in droves, asking for Connor’s story.
...
Series have become extremely popular, and secondary characters are now in the spotlight.
...
Because series are a huge part of the market now, when creating the first book, make sure you sketch out who will appear in your follow-ups.

(https://janefriedman.com/writing-seco...)

An excerpt from Write Naked: A Bestseller’s Secrets to Writing Romance. Who's the author?

Jennifer Probst is the NYT, USA Today, and Wall Street Journal bestselling author of sexy and erotic contemporary romance. Her book, The Marriage Bargain, was ranked #6 on Amazon's Best Books for 2012, and spent 26 weeks on the NY Times bestseller list.

What? Series again? Thoughts?

[Ian]

The interesting part of this question is whether a secondary character in one book in a series should remain so? I have a five book "series", and I started the writing with episode 4. (If Lucas can do it, so could I!) Except in my case, it was intended as a standalone book. The problem then was that one of the secondary characters obviously had a backstory that was rather interesting, so later I wrote the three in which the secondary character became primary. The fifth was always intended because my SciFi books all have a background of governance - each one has more or less different forms of governance, and the fifth was my theocracy, and in this, a secondary character from the 4th is one of the main ones in the fifth. They were not published in this order, though, but rather the order of timing, so it gave me the chance to manipulate a little in episode 4. In my opinion, a complicated series really has to be essentially written, at least in draft form all the way through before any is published, otherwise there is a tendency to dig holes for yourself.

[Graeme]

If you have a long series. Multiple strong secondary characters are essential. Breathe a powerful purpose and a nuanced personality into them and let them roam.

[Graeme]

@Ian. Long series = lots of planning. Agreed.

[Quantum]

but what if it's not a sequence-dependent series? that doesn't take as much planning and a secondary character can actually become an MC in another book, correct? The sci-fi, the Culture series (of which Inversions and The Player of Games were recommended to me) comes to mind as a wide-ranging "fairly" sequence-independent series.

[Graeme]

If the books are independent but set in the same universe than you can pretty much do anything.

[Ian]

Graeme wrote: "@Ian. Long series = lots of planning. Agreed."

Yes, if the following depends on what has come before. If they are independent, it probably does not matter.

[Marie Silk]

I had a secondary character who ended up getting her own story by book #4. Honestly, I had no idea if readers would even be interested, especially since I had to go retroactive in the series timeline. It turned out to be my book with the most favorable reader response of all! Also it is my personal favorite from the series. I thought it would be my last book to the series, but the characters decided differently. Sometimes you gotta take the risk and see where it goes :).