In "The Most Dangerous Game," are the main characters flat or round?

Flat characters are characters that have one or two
characteristics and are not fully developed, whereas round characters are ones that are
developed and we are allowed to see them as complete characters. Going by this
definition, it is clear that both General Zaroff and Rainsford are round characters -
they are characters who are presented to us in completeness - we are allowed as readers
to understand what is going on inside of their heads, especially Rainsford. Although we
get little information about Zaroff's internal workings, we are shown his motivation for
setting up the "hunt" or the "game" that dominates the end of this
story.

You might like to think about some of the other
characters to enable you to see the contrast. It is clear that Ivan, the Cossack servant
of General Zaroff, is a flat character - we have little access to his thoughts and he
really only serves one purpose which is to look big and menacing and serve
Zaroff.

Hope this helps you understand the difference a bit
better!