Now that you’ve decided what your character’s motivation is, it’s time to actually construct the vessel in which this purpose will reside. Just how do you build a person? By creating a life where none existed. Start at the base, and work your way up:
How was the character’s early life? What was the person’s family like? It doesn’t take much effort to stray too far into pop psychology, but household composition and environment have a significant bearing on personality. So does one’s experiences in school and in social settings as a child and an adolescent.
Is domestic trauma in the character’s past? Social stigma at school? An unusual amount of teenage angst? Were they abused, neglected, spoiled, enriched? Were they denied a childhood, or unable to outgrow it? You don’t need to write your character’s biography, but you should know the outline.
Is the character a loner, or a social butterfly? What type of family and friends does the character have? How do they interact with acquaintances and strangers? Do they have a romantic relationship or casual sexual partners? If they’re gay, are they out, or closeted? Are they extremely close to a few friends, or do they have a wide but shallow social circle?
What does the character do for a living? That may be integral to the story, or it may be incidental. Readers deserve to know, though. But don’t lock in a stereotype. It’s easy to associate personality traits with certain professions or pastimes. What’s not so easy — but is oh, so satisfying — is to cast against type: How about a happy-go-lucky private eye? A softhearted crook? A wizard who can’t spell straight?
Do they like their job? Are they fulfilled, or frustrated? Good at what they do, or inept? How do they relate to those above and below them in the workplace hierarchy? Do they lie, cheat, or steal, or are they a paragon of productivity? Either way, are they rewarded, or punished, or ignored?
What does your character do after work, on weekends? Where do they vacation? What are their hobbies, interests, passions? Do they have an eccentric or unexpected avocation? Do they have a remarkable skill or talent no one knows about? Are they philanthropic or charitable, or is all their spare time given to family and friends, or are they devoted only to themselves?
Is the sun always shining, or does a perpetual rain cloud perch just over the character’s shoulder? Are they blithe, cheerful, confident? Suspicious, resentful, fearful? Whether your character’s glass is half full or half empty will determine the story’s tone, so check the person’s beverage before you put fingers to keyboard or pen to paper.
What are your character’s political views and social opinions? Are they religious? Skeptical? Atheistic? Scientifically minded, or superstitious? Are they charismatic, or a wallflower?
So many questions! But so many answers must be provided — and many more must be discovered on the journey that is the act of writing. (And some answers may change.) This character design is essential to your success — not just for your main character but also, to varying degrees, for major and minor supporting players and for walk-ons. Whether you’re aiming for high literature or genre fiction, the extent to which you care about your characters and their personalities will in large part determine how readers respond to them.