Which character is the most powerful in this novel? Which character is the most powerless? How do characters react to being powerful or powerless?

For a time the reader feels that Randle has the power now that he has disrupted Nurse Ratched's tyranny and made the men feel more like individuals and people who can make their own decisions.  However, she holds the upper hand when is able to have Randle lobotomized and even though the Chief has gone through the wall, he will never again hold power as she does.  Ultimately her power resides in her cruelty, and the inmates simple bow down to that cruelty because it is ultimately less painful.