Secondary character should have a distinct role in the story in order to avoid becoming filler and getting lost in the greater plot.
The role of a secondary character should NOT exist only in relation to the main character. This creates flat characters who are difficult to develop into more meaningful elements in a story. Consider why a secondary character is involved with a hero/villain and why he or she continues to associate with them. Taking a deeper look at motivation can help confirm their role in the overall story.
A secondary character with a strong sense of duty may struggle to disentangle themselves from a main character making harmful decisions, or a secondary character who is a friend and coworker of the main character may be riding that character’s coattails of success in hopes of moving up themselves. The deeper you dive into why a secondary character exists in a story and how he or she will impact it, the more engaging and interesting the character and story will be.
It is very easy to fall into stereotypes with secondary characters. Stereotypes can be a good starting point, but should never be the end development of a secondary character. Be mindful that you are not pigeon-holing a character into a role such as the comic relief, love interest, lovable rogue, wise old mentor, token diversity character, etc. If you can describe a secondary character in a few words or less, he or she needs further development. Where did that most noticeable characteristic come from and what purpose does it serve for that character?
A secondary character’s thoughts, actions, and choices should be largely based on their own needs and desires and not always fall back to what the main character needs or wants. While secondary characters do serve to aid the development of the main character and move the story along, be sure to weave in his or her own development and progress. This will add important layers of realism to a story.
If you aren’t sure yet why a secondary character might do or say something, take some time to create a backstory for him or her. You may not use most of the backstory information you develop, but it will help you better understand the character and write them in a more realistic and relatable way. The backstory may only be a paragraph or two, but it helps cement that character as an individual in your mind while writing.
Understanding a secondary character’s role in the story will help you better integrate them and make them stand out as memorable and interesting to the reader.