in "Shawshank Redemption", why are minor characters like Brooks and the Warden important, and what are their characteristics (evidence).

Minor characters occupy a great deal of importance in the King work.  One such way is that they help to evoke much of the thematic relevancy of the work.  For example, Brooks becomes the example of how life is something that lies within the individual.  The notion of an "institutional man" becomes defined by Brooks, making his presence in the work powerful.  It represents the initial opposition between Red and Andy, a distinction that becomes fused through understanding at the conclusion of the work.  The warden's role, as well as much of the prison staff, is present to show how corruption is present, bringing humanity to the prisoners and a sense of inhumanity to those who are intended to uphold the law.  Side characters are used in the work to illuminate the themes and concepts that are explored throughout the story.