Writing and the Supporting Cast

It's a rare story that follows one person's adventure from beginning to end without much interaction. Usually our protagonist has encounters and situations along the way, or at the very least has internal discussions to help expand the character's thought process. But more often than not, our hero will come across a wide variety of other people along the way. We've talked a lot about writing the hero's journey, so now let's give some time to the supporting characters.

The first rule of creating the rest of the cast is knowing what their purpose is. Of course, this means the first mistake of writing is making these other characters little more than means to an end for the hero. If everyone else merely provides information, clues, challenges, or obstacles for the hero, then they become one-dimensional vendors of plot progress. Furthermore, the main character misses a chance to gain some depth by showing a two-way interaction with those around them. Without this, the hero seems self-engaged, narcissistic, and a social island unto themselves. If that's what the author wants, then fine. However, a reader often wants more.

So now that we've decided to give purpose to our supporting cast, let's look at some of the different roles they can play:

• Voice of reason: As our hero goes forward, are they on the right direction? Are they acting on emotion rather than practicality? Do dangerous forces exist, such as revenge or greed? The Voice of Reason character can provide a centering force when things are getting out of control. This is best shown through a hero's trusted friend, mentor, or someone whose words carry weight, and might make the hero think twice.
• Devil's Advocate: This is similar to the Voice of Reason, but instead of being a steadying force, the character represents any drive that would work against the hero - impulsiveness, anger, a corrupt sense of justice. This challenges our hero to assess every motive, and even doubt themselves. These characters allow the main character to reach critical points of realization, which allow growth and progress. And of course, backsliding or making the wrong choice is always allowed.
• The Road Not Taken: Part of any hero's journey is to go forth into unfamiliar territory and experience things that invariably change them forever. The character of The Road Not Taken is a reminder of what the hero is leaving behind - for better or worse. If the hero is taking risks, then this character shows security and stability. A hero investigating the past would be confronted by someone representing the acceptance of the status quo. The Road Not Taken should be inviting in some ways, offering both the advantages of the old life along with the downsides. At the hero's lowest point, that character should be very inviting, and leave the hero conflicted - or perhaps aware of why his journey is that much more important.
• The Possible Future: As our hero goes on their journey, is there someone who represents the ideal outcome? Is there someone they idolize? Someone who personifies what they expect at the end of the rainbow? The Possible Future character is very important, particularly because this can represent what the hero thinks the outcome should be when they start, but not what the hero discovers. This allows us to show how the hero grows throughout the novel, and how learning about themselves changes how they see what is important. Often, The Possible Future is no longer desired by the end of the novel because it only seemed good before the character learned about the world and about themselves. 
• The Greek Chorus: This is a catch-all for characters who will reflect pieces of the hero. The hero can respond to them, which allows the reader to see potential internal conflicts that are not fully recognized. If our hero has trouble with relationships, there can be a Greek Chorus character who just destroys any relationship they enter. How our hero responds to this character says everything about the hero, and shows the reader the conflict within the main character. 

There are plenty of archetypes that can also be used to show a particular facet of the story. Any character who enters the story, however, should provide a chance to advance the story and to move along the hero's journey. If they don't move things along, what's their real purpose?