A complex character is a character who has a mix of traits that come from both nature and experience, according to fiction writer Elizabeth Moon. Complex characters are more realistic than non-complex characters.
According to Elizabeth Moon, the traits of complex characters are made up of both constants and variables. The constant traits are the innate ones, such as eye, hair or skin color. The way a character reacts to these traits adds to his personality. The variable traits come from life experiences and how the character reacts to those experiences. A character's reaction to a situation may change over time as he develops. Development also plays a large part in complexity; just like a real person, a character changes as the story goes on.
Angela Ackerman of Adventures in YA Publishing says that flaws play a large role in a character's complexity. Characters should not be perfect; they should have a few flaws that add to their personalities and make them more realistic. When characters interact with others, they may point out their flaws or ignore them, just as people do in real life. It is also important to know the reasons behind the flaws to make a complex and realistic character.