Could be anyone; your spouse, parents, siblings any other member of your family, your friends, acquaintances, neighbors, classmates, teammates, childhood friends,…
Perhaps the only requirement for this method to work is that you think you know your model.
Physical Appearance
This should be the most obvious but very helpful application. Just describe your character as you would describe your childhood friend, for example.
You can always change a trait or two, like hair color, weight, height, especially if you want to disguise your methods and make the character unrecognizable but realistic. Just remember what you’ve changed and coming back to your character’s image should be easy.
It’s a very useful trick if you plan to have a lot of characters, just make a note next to your character’s name; something like –
Will Collins (looks like Johnny, my classmate, but with curly hair).
The next time you have Will in your scene, you will immediately know that Will Collins looks exactly like Johnny, but instead of straight he has curly hair.
Backstory
Having a character with a physical description and a backstory is a job half done when it comes to creating a character. It saves you a lot of time which you would otherwise spend creating these traits, but I must advise you to be careful with the backstory.
For my first novel, I used a backstory of my childhood friend and I didn’t ask for permission.
Namely, he once told me a story of him meeting his father who left his family when my friend was still a child. They’ve met after more than 10 years of separation. That event was very stressful for him and I remember the exact words that he used to describe his feelings:
That wasn’t my father. It was an unknown man who looks like my father.
His story was so powerful that I couldn’t resist.
The awkward moment happened after I’ve published the book. He called me to tell me that he’s coming to town and that he wants to buy a signed copy of my book, for his mother and his sister.
I needed to explain myself, and luckily he was glad that I used him as a character for my book. After he finished reading, he called me and told me how much he cried and that he liked the story.
Therefore, a backstory of your friend is a great tool, but make sure to let people know what you’re doing.
Likes, Dislikes, and Vulnerability
If you spend time with someone and get to know that person, you learn what they like and dislike and what can cause pain to them. Knowing these facts about other people, makes you behave differently in their presence.
If you care about someone, you would never offer a steak to your vegan friend, you would never mention death in a presence of someone who’s just lost a family member, and you would always say how great that Liverpool match was if you know that somebody is their true fan; and you would never invite you vegan friend and your carnivore friend to the same dinner; unless, of course, your intention is to hurt someone’s feelings.
In the same way, if you know these facts about your characters, it would be much easier to plan their desires, conflicts, preferences, and to make realistic interactions with each other.
Predictable behavior
If you know someone long enough, you can probably predict their behavior. That’s why couples or siblings, or really good friends, tend to finish each other’s sentences; one simply knows how the other person thinks and feels.
So, if you play the card of modeling someone who you truly know, you will have the ability to predict their behavior.
This is strongly correlated with the dislikes, likes, and vulnerability but goes a little bit deeper; it gives you the ability to walk in other person’s shoes, to feel and think like them. It’s not simply knowing certain facts about that person.
Put them in extraordinary situations
The fun part about using your friends and family as the book characters is the ability to put them in extraordinary situations.
You get to ask yourself how would someone react if their lives were endangered; if they lost someone; if they kill someone; if they steal something; if they need to get out of somewhere… and you simply create story by thinking and acting like they would.
They won’t know
If you still worry whether they’ll know that you used them as a book character, just stop. They won’t know unless you used the exact story and their real names.
If you tweak just a little bit, like hair color, hairstyle, name, and add a peculiar detail, like a scar, tattoo, stuttering, or a common phrase, they wouldn’t notice.
After all, it’s your image of the people you are using as characters. They have their own image of themselves and there is no way that these images would match 100%.