Interesting relationships among characters are a fundamental part of any good story. No less so in a good thriller. In fact, characters who really care for each other but are separated by insurmountable obstacles add to the thrills and the action. I'm not saying it’s easy, because in this genre the plot tends to drive and inspire the characters — they're motivated by extraordinary events thrust upon them, usually with a very limited time to resolve the situation.

I met best-selling author David Dun at ThrillerFest in NYC who says that good character development magnifies the suspense. The thriller, he says, examines character in the crucible of extreme stress more than it USES character for suspense. “How can we care about someone’s peril if we care nothing for them?” he asks.

Still, Dun says that thriller stories don't seem to spend much time exploring a character's quiet desperation, or their compulsions and the consequences. In a thriller, he says, when authors treat readers to a display of a character's insanity, “...we're using it as a device to put readers ever closer to the edges of their seat rather than create a personal epiphany about life or its meaning.”

You can read Dun’s article: “Character, Genre, and Other Incidentals.”