A Character walks into a bar ... 8 elements to design an engaging character

Characters are the backbone of every story. An interesting character is complex and layered. They start out as one thing in the beginning, and through the crucible of story, they morph into something new. They have flaws and strengths and the two play against each other. Interesting characters have agency in the story, and their choices have consequences.
Creating a character with agency can feel a bit daunting. You, as the writer, want to control the outcome so that the story goes in the direction you desire. A well-designed character will refuse to cooperate if you try to force them into a choice that goes against their design.
But, you're the writer. You can make them do anything. Right?

True. But, part of our jobs as writers is to create believable characters. Readers will only suspend their disbelief for so long before they toss the book across the room. That means you need to listen when a character refuses to do something. You need to dig into their DNA to figure out why they don’t want to cooperate. Some writers have elaborate methods for creating characters as they create everything from genealogy to elaborate back stories before they ever set pen to paper. The method I’ve chosen is simpler but as deep. Its focus is on boiling the character down to their basic needs and motivations in the story.
1. Strengths

Strengths are the traits that will help the character achieve their goals. Strength does not mean physical strength. While muscles can be helpful, I am referring more to strengths of character. These are attributes that are favorable and work to help the character achieve their goals. Cunning, intelligence, witty, friendly. These can all be strengths. They can also be weaknesses depending on how they are used.
I have a character who is a private investigator. His job requires a certain level of intelligence and tenaciousness for success. He also needs to be able to read people. He's observant and cunning. But with these strengths comes ...
2. Weaknesses

Weaknesses should ultimately play against the character's strengths. They are the traits that most often lead a character into failure. My cunning and intelligent PI is also a cynic, and his snark tends to get him in trouble when he opens his mouth at the wrong time.
Weaknesses are what set the character up for failure. Characters need to experience failure within a story. Failure drives up tension and conflict which helps to move the story forward and creates motivation for the character to step up their game.
3. Desires

Think of this as your character's personal theme. What is it that they want? What drives them? What is their ultimate goal? Knowing this ahead of time helps you avoid a character that feels inconsistent or waffles when opportunities are placed in front of them.
Desire is different than need. A character's desire is the big picture goal. A character’s desire isn’t an “in the moment” sort of thing. This is the BIG thing they want. The underlying motivation behind every decision, every action, and reaction. Revenge for the death of a loved one. Social justice. Acceptance by peers. Love and safety. This is the one thing they are always aiming to achieve. It plays in the background like personal theme song for the character. It is the goal that makes them reach outside their comfort zone and move toward a new reality.
4. Moral Choice

This is the key choice that character will need to make to get what they want. This will be the choice that ultimately completes their arc. Revenge versus forgiveness. Stick to beliefs or compromise them to achieve the goal. Save the enemy or let them fall to their death. The idea is boil down the character’s story line to this key choice. When you know what that choice is going to be, then you as a writer can design a character that will inherently make the choices you want them to make. You will be able to see what strengths and weaknesses they need, what kind of moral fiber they need.
5. Action

Action is what the character does to reach their desire. What they give up or do to make their goal a reality. My PI takes an intriguing case which embroils him in political and magical machinations which force him to face the life he left to become a PI. His ultimate desire is to find fulfillment in life. In being forced back into his old life, he reconciles his past with the new life he has built which ultimately culminates in him finding the fulfillment he seeks. Understanding the action a character must to take to reach their goal will help you better orchestrate the events of the story.
6. Changed character

Where does the character end up? Knowing what the end of the character arc is before you start gives you a target to aim for. It allows you to shape events that allow your character to grow or fail depending on their arc. It helps you to steer the story in a believable direction. In one of my projects, I have a character that is desperate to save his charge. This desperation steers him to make a choice that puts his charge at risk. In the end, he redeems himself. The arc is a tragic one, but knowing that his changed character will risk everything to fix his mistake helps me foreshadow the end of the story.
7. Need

Need is what the character has to change within themselves in order to achieve their goals. Need is different than action. Need is the mental changes that must occur for the character to reach their end point. For our royal in exile, this need would be developing the confidence to stand up to stronger personalities. It is the mental change needed to complete the arc.
8. Problem

This is the ultimate problem of the story. The obstacle your character must overcome to reach their goal. It is what stands between the character and everything they want. It is a combination of the character’s personal weaknesses combined with the antagonist’s desires. The problem is what churns out choices for your characters. Choices are what the character needs to succeed or fail. Because with choices come consequences - good or bad - and that is what creates the events that move the story from point a to point b.
Notice that many of these things overlap. Strengths are linked to weaknesses. Moral choice to the changed character and the desire. Need is linked to the desire and action. That's purposeful. They build upon each other to create a nuanced character that may or may not succeed depending on their goal. To be believable, the story problem must be linked to all of the other pieces. And that brings us to how to use this in your story …
Building Back Story

I'm a pantser. Which means I don't create back story until I need it. Some people write elaborate back stories using templates and sheets and a plethora of short stories for every major event in the character’s life. There is nothing wrong with either approach. The important part of back story is coming to terms with the fact that 90% of what you create will never make it into the actual story. It will be revealed through a character's passions, prejudices, fears, and actions/reactions. This is important to remember because all of this work in designing the character is the same. It comes out through the character’s actions, reactions, choices, etc. Character design becomes the character’s DNA. It is the invisible force that guides the character in everything they do.
Connecting the protagonist to the antagonist

Designing the antagonist is as important as designing the protagonist. The antagonist needs to be as thoroughly developed as the hero. This creates conflict and tension. Friction occurs naturally when you have two fully developed personalities with opposing goals or similar goals, but opposing ideologies. Give your hero someone to really challenge them. Develop the antagonist of the story as fully as you do the protagonist. Everyone is the hero of their own story. So make sure to do the villain justice by making them as nuanced as the hero.
Connecting supporting character to the protagonist

Similar to the antagonist, creating fully realized supporting characters lends depth to the story. It creates opportunities for conflict and allows you to explore multiple sides of the story problem. This doesn't mean you need to write from the supporting characters point of view. But giving them their own goals within the story lends authenticity to the supporting cast. They become characters that the readers can care about, cheer on, and boo alongside the hero and villain.
If your characters aren’t cooperating or your story hits a brick wall, chances are good it comes down to your character’s DNA. Something was forgotten, was inconsistent, wasn’t a strong enough choice, or got left out of the character’s design. Working through their design elements can help get the story back on track.
Happy Writing!