While a fictional character emerges from an act of imagination, fiction is grounded in lived experience. And in turn, the best fiction both reflects on and gives meaning to our shared lived realities.
While a fictional character is necessarily not real, and many even exhibit fantastical or superhuman attributes, in the best fiction, a character or protagonist should resonate with the reader. And in so doing, the character should entertain, move a reader, and ultimately provide a mechanism for reflecting on some aspect of the real world or the reader’s experience of it and of themselves.
For a character to resonate, they don’t have to be like a real person, or even act like a real person. But there have to be sufficient elements that tie them to the lived experience of readers, thus rendering the character believable.
For instance, a character’s appearance should more or less reflect (some aspects of) expectations and norms for that particular character, such as gender, age, dress, and ethnicity attributes. Similarly, a relatable personality, and reactions to story-events that are in keeping with that personality, facilitate believability.
A character’s personality is often discussed, in fiction, in terms of “voice”. This is communicated by a skilled writer using vocabulary choice, paralinguistic cues (such as apt descriptions of gestures and facial expressions), style of dialogue, and other cues, including the character’s outlook and assessment, both on the story-events, and on life more generally. These elements all serve to give a well-rounded feel for the character, making the character “feel” fully developed.
What is also important is that the character’s emotional responses to events, and their goals, should be grounded in everyday (non-story-world) logic. A character should react to story-events in keeping with reasonable norms as to the standard types of experienced emotional valence. If a character reacts emotionally in non-standard ways, that is not a logical consequence of the character’s personality or goals, then this can jar, and result in the reader not feeling a connection with the character.
Finally, and of the utmost importance, is character development. To successfully resonate with a reader, a character must learn, make mistakes, and evolve—whether for better or worse—just like an ordinary person. A character must experience danger and challenges—whether physical or emotional—and react in a way that is in keeping with the character’s personality and goals. All these things help make a character believable.