Captain Coles is a boss in name, but not in attitude. There's nothing bossy about Captain Coles: he's just a good family man trying to get everyone home in one piece.
He's in charge of the Civil Affairs unit that Birdy and his friends are in. He also rides in the First Squad Humvee with Birdy, Jonesy, and Marla, so Birdy gets up close and personal with him during combat. And (no shocker here) he's basically awesome the whole way through.
Coles is an authority figure Birdy trusts. He's described as "tall and thin with blue-gray eyes" (1.4)—not exactly the most imposing description, and in the same paragraph, readers are told he "always looked sincere" (1.4). The guy keeps it real.
Though we only learn pieces of the other characters' back-home lives, Coles mentions an important detail of his home life right away:
"My personal mission in life is to grow old and grumpy and watch my kids flunk out of school." (1.32)
He's a dad, and that role is important enough to him to tell the soldiers under him that his kids are his reason for staying alive. Aww, shucks. That's sweet.
Because most of the unit are teenagers or in their early twenties, Coles shows readers another perspective—what it's like for a parent who is serving in the active military.
In the middle of the story, his three-year-old daughter is hospitalized, leaving him feeling helpless. He doesn't say too much about it, but the situation makes Birdy think,
It didn't seem fair, in a way, that everything back in the real world was still going on while we were in Iraq. (12.90)
Coles has enough to worry about (what with keeping everyone alive and all), that it feels like too much for him to have a sick kid halfway around the world on top of that.
We never find out what exactly happens to Coles' daughter, but Birdy does witness a realization that Coles has. Coles tells Birdy that war teaches you things.
"What it's taught me is that I love my wife and family more than I knew, and a lot more than I ever told them." (13.40)
That's how you know he's a good guy—the biggest lesson he learned isn't selfish. It's about how he should treat family.
It's Coles' job to make sure each mission is completed, so he can be tough at times. He starts the book by giving Robin a hard time about his name, and he gives the orders. He isn't tough for no reason…but when something needs to be done, he makes his soldiers get in line double-quick.
He does this, in the beginning at least, because he believes in their mission. He says,
"I feel good about defending my country, about being in Civil Affairs. You know, we bring a human face to war. I feel good about that." (2.21)
But like his soldiers, Coles gets more and more uncomfortable with their role in the war.
On their last mission, after Roberts orders them about their mission to "return" children that the U.S. side had kidnapped, Coles admits,
"In a way we are getting closer to the people we're dealing with. I don't trust Roberts either." (14.332)
Basically, he's reached the point when he relates more to the Iraqis than he does to his own higher-ups. But what can he do? Coles gives the orders and leads Roberts' mission. Because he's like that—thoughtful, but ultimately dutiful.