Characters are important, but no more important than any other part of your story.
Interesting characters in stories with no plot are not going to be interesting. Great plot with interesting characters but no thematic point may be entertaining, but ultimately not very satisfying or impactful.
In order for a story to have the power to make a strong argument and to affect its audience, a writer must draw the connections between a story's characters, plot, and themes.
Dramatica helps guide you as to the reasons why you will select certain characters that are appropriate for your story's plot and themes.