How To Write Killer Characters
Developing characters as fully formed, three-dimensional people requires patience, observation, and knowing what to put on the page and what to keep off. Here, author Marnie Riches shares how to write killer characters.
The Lost Ones is my 10th crime thriller and the first book in my fourth series. Writing series that will keep selling, beyond the fanfare that surrounds the first book, demands a particular skill, and that’s the ability to write killer characters. If you’re penning a standalone, you have to have believable characters and a main protagonist that readers will root for, but with series it’s doubly important, because you will have to sustain a developmental arc for all of your characters over the course of several books. Great characters will provide the answer to the question: Why should I care enough to keep reading?
When I wrote my award-winning debut novel The Girl Who Wouldn’t Die in 2009, I had no idea that I would be signed up to pen three novels in that series and a further two, under a subsequent deal. My main protagonist was Georgina McKenzie, the young, aspiring criminologist who has to divide her time and energies between the academic world of Cambridge University, the gritty urban grind of Southeast London where her aunt lives, and Amsterdam, where she eventually works with the Dutch police as a criminal-profiler.
Without realizing it, I had created a character with a thoroughly believable backstory (unsurprising, since much of that was inspired by my own upbringing), whose abrasive personality naturally generated drama whenever she came into contact with authority figures. She had career plans and emotional trauma to resolve too, which gave me somewhere to go with her story.
As the series developed and she aged, I was able to delve deeper into her past and show how her uneasy relationship with her mother served to make her difficult and outwardly feisty but inwardly vulnerable, yet she also demonstrated an inner steel and determination to do right and change the course of her life. I think that series was successful because George was a flawed individual, who was nevertheless wholly identifiable and compelled the reader to root for her. And those are the basic ingredients for any good leading character. You’ve got to ensure your hero is 3D.
Once you’ve figured out who your main protagonist is, you need a raft of supporting characters who are similarly compelling. They should all say something about your main protagonist too, in the way that they relate to one another.
In The Lost Ones, I’ve created a new leading lady called Detective Sergeant Jackson Cooke—Jackie to her pals. She’s an older mother of twin 10-year-old boys, one of whom has suspected ADHD. She’s also into her third trimester of pregnancy and still working. I wanted to portray a scenario which many modern women struggle with—being Momma Bear at home and a go-getting Rottweiler at work in a man’s world. Jackie’s newly retired mother, Beryl, lives in the basement of her house and has an antagonistic relationship with her daughter because of a past family tragedy. Husband, Gus is an amateur musician and stay-at-home dad, who doesn’t do his fair share of parenting or putting food on the table, yet his frustration at the long hours that Jackie works as a murder cop is justifiable. Jackie’s boss, Tina, is an ambitious Inspector who is far better at internal politics and PR than she is at meticulous police work. She sees Jackie as a rival. All of these supporting characters serve to demonstrate that Jackie is loving, conflicted, overburdened, frustrated, proud, and diligent.
When you’re penning your cast of characters, make sure you’ve invented little backstories for all of them—though you needn’t incorporate these into the narrative. Your depth of understanding of your characters will shine through when you write. You’ll know that they love mac and cheese but hate Oreos; they’ll have a pathological fear of heights and will be murderously shy but will happily get on stage to belt out a karaoke classic. They’ll be just like real people!
This leads me onto my next point, which is the dos and don’ts of character portrayal. Do show that your character is gregarious and boastful by having them dominate a conversation where they brag about their car or their abs or their holiday in Hawaii’s premier resort. Don’t say, “John liked the sound of his own voice too much and boasted constantly.”
Do show that your character is feeling nervous by depicting their body language—perhaps a sweat breaking out on her top lip or her playing with the hem on her sleeve or his foot bouncing. Don’t say, “Gloria was nervous.” Better to show us Gloria’s twitching eye when her boss walks in the room. It says far more about her character, and crucially, allows the reader to fill in the gaps for themselves. Show, don’t tell!
Dialogue is super-important when creating a killer character. I teach creative writing and this is where students often fall down. Decide in advance, in your head, what your main protagonist and the people around them all sound like. Do they have a Southern drawl? Do they speak in a brusque, hurried fashion like a New Yorker? Are they taciturn, speaking in an economical way? Do they love to gossip and go on and on and on? Listen to how real people speak on the bus or in the supermarket. Eavesdrop, and remember how those chatting friends or sparring enemies sound.
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If need be, watch fly-on-the-wall documentaries, where real people speak to one another. Don’t try to faithfully transcribe accents and especially avoid representing stereotypes of accents. Instead, listen to the rhythms of speech and try to emulate those. You can and should write characters who are different from you, but make sure you’ve done a good job of listening to real people first.
The golden rule of creating compelling characters is that in the course of a story—be it a short story or a novella, a standalone or a series of 10 books—you should surprise the character and your reader. Whether you write romance or serial killer thrillers, like me, chase your main protagonists up a tree and throw rocks at them. For the reader to believe in your killer characters, there needs to be drama and tension in the story, where your characters face problem after problem and then overcome those issues.
This will give you a dynamic story and characters that grow as people. This will avoid the pitfalls of creating two-dimensional cardboard cut-outs and having zero narrative tension. Remember: All story should come from character, so be really careful when you’re writing to give your characters the attention they deserve. Over time, they will feel as real and familiar as old friends!

Marnie Riches grew up on a rough estate in north Manchester. Exchanging the spires of nearby Strangeways prison for those of Cambridge University, she gained a Masters in German & Dutch. She has been a punk, a trainee rock star, a pretend artist, and professional fundraiser. Her bestselling, award-winning George McKenzie crime thrillers were inspired by her own time spent in The Netherlands. Dubbed the Martina Cole of the North, she has also authored a series about Manchester’s notorious gangland as well as two books in a miniseries featuring quirky northern PI Bev Saunders. Detective Jackson Cooke is Marnie’s latest heroine to root for, as she hunts down one of the most brutal killers the north west has ever seen at devastating personal cost. When she isn’t writing gritty, twisty crime thrillers, Marnie also regularly appears on BBC Radio Manchester, commenting on social media trends and discussing the world of crime fiction. She is a Royal Literary Fund Fellow at Salford University’s Doctoral School and a tutor for the Faber Novel Writing Course.
Visit her at marnieriches.com, and find her on Facebook, Instagram, and Twitter.