A character can be defined by other characters that are surrounding it. This doesn’t mean just the supporting cast of friends they have (or don’t have); the characteristics of those folks and how they work with the character in question goes a long way to identifying aspects of the character in question. Are the connections built on common bonds? Is the character in question just using other characters; if so, what do they gain by doing so and how does it reflect on the character?
Also, antagonists that a character faces also help mold this definition of who the character is. What are the reasons that create conflict between the character and the antagonists? How easy or difficult would resolution be for them.
Think about these the next time you read or write and challenge yourself.
Until next time!