Here's an excellent excerpt from Bob Buck, "North Star Over my Shoulder", Simon & Shuster, London, 2002, Chapter 1, pp 22-23.
"I lean over the counter for a closer look at my crew list and note that O.B. Smith is tonight's first officer, copilot, which makes for a warm feeling because O.B. is quiet, efficient, and a pleasure to be with.
A copilot can make a trip or ruin it; get someone who talks too much, gripes about the company, tries to impress you, tells long and boring anecdotes, or is overly aggressive in suggesting ways to run the flight, and the taste is unpleasant. Al was one of those. He was a captain on domestic, but bid copilot international on the 747 because it paid more and had the romance of flying to Europe and other distant places. But he couldn't stop being captain and started tuning radios and adjusting navigation items without telling me. I finally had to lecture him strongly: "You bid copilot, now #### it, be a copilot and not a captain. We'll do things my way, and if you don't like it go back to domestic". It worked and he settled down, but his resentment always showed.
Now and then there'd be a milquetoast who wouldn't get things done unless you told him each item you wanted. A good copilot is a balance of these things, following, doing as told, but strong enough to point out any error you have made.
All in all my copilots were fine, like O.B.: a big man from Iowa farm country who came to flying via the navy. (for some reason, naval aviators always seem to be from farms, way out in the middle of the country, far from the sea.) Farm people impress me because they generally have common sense, and if there's one trait a pilot should have in abundance it's good old-fashioned common sense. Farm people also have a way of recognizing that certain things, even unpleasant things, have to be done, they don't ##### about the chore, or cuss out the company because of some obnoxious procedure, and they don't get vocal or outwardly scared when things get tough like the weather going down......."
"If that were to happen, O.B. wouldn't change appearance a mite; he'd just settle into computing fuel, getting weather information....."
"Yes, it's a good feeling to have O.B. in that right seat beside you."
There's lots more on the topic of captain/copilot relations in this book that is just plain right on the money.