In fiction, a feeling of authenticity tends to emerge from characters who are complex, idiosyncratic and flawed. This prompt is not about the deepest secret or the one terrible or great thing that motivates your protagonist but smaller level details that will add authentic granularity to their character.
Write several paragraphs with several new details about your character detailing a few of the following:
An small incident they have never told anyone in which they once did something that seems at odds with their present public persona — something cruel or debased for an overarchingly good character, something tender for a harsh character, something narrow-minded for a typically open-minded character, that sort of thing, or simply something so atypical for them that no one in their current life would believe it.
A totem object that is important to them because of what it represents.
Something they lost a long time ago that they still think about.
Something they hide to protect it.
Something they hide because they are ashamed of it.
Something offensive that they have done or said.
Something that offended them.
Can you write about an offensive act or statement without making your text offensive?
Don’t dump these all in the same place. Keep them in you narrative storehouse and sprinkle them in when you need to add complexity or depth.