Our parents, friends, where we live, what we see on the news, the music that we listen to, the shows that we watch on t.v., etc. Our preferences, things we like to do, our experiences.
Sometimes all of our protagonists end up being our age, or are from a similar town to the one we grew up in, or have the same kinds of life experiences
The flip side is also true: who you pick for your protagonist determines who your readers root against. The person or force directly opposing your main character becomes the enemy in the reader’s mind.
In Lucifer, the audience is against his father (God).
Who your protagonist is also controls the tone, emotional journey, and type of story. Pick any superhero movie recently produced. If the villain were the protagonist, the story would be a tragedy because they failed.
If you choose first person or third person close, your readers will see most of your character’s inner thoughts and emotions. This gives the reader greater insight into why your character does what s/he does.
Third person close is still intimate with the main character without being inside their head for the whole story.
Born mute, speaking only in sign, Edgar Sawtelle leads an idyllic life with his parents on their farm in remote northern Wisconsin. His parents, Gar and Trudy, raise and train a fictional breed of dog whose remarkable gift for companionship is epitomized by Almondine, Edgar's lifelong friend and ally. *Dr. Papineau is the vet