Who is the main character in The Bell Curve: Intelligence and Class Structure in American Life by Richard Herrnstein?

There is no particular main character. Perhaps the main focus of The Bell Curve is on what the authors term 'the cognitive elite'. The cognitive elite are those members of American society that both have high IQs and positions of power, influence and resources when it comes to occupation. They are elites in the sense that they are smarter and more powerful than the large majority of Americans.