In general, the people who wrote the Constitution came from the elite of society. They were certainly not representative of the population as a whole. This is why some historians (most notably Charles Beard) have argued that the Framers created a constitution that was biased in favor of the elites.
There were 55 delegates who showed up at the Constitutional Convention at any point. There were never more than 38 there at one time. These men were typically from the elite of society. More of them were educated than was true of the general populace. More of them were wealthy. Almost all of them had served in important governmental positions. Many of them were rich enough to have many slaves. Others were speculators in land and finance. There were merchants and other such relatively middle-class people among them, but the group was generally skewed towards the elite side of society.
This is relevant because the Constitution that they produced was a somewhat conservative document that seemed to favor the interests of the wealthy. This might well have been good for the country since it gave it a strong foundation for economic growth. However, it does lead some historians to claim that the Framers were looking out for their own economic interests and those of their class, not for the general popular welfare.