He is the narrator of the novel, so the reader is privileged to understand how sane he really is, despite the fact he has been subjected to horrible electroshock treatments, which are administered more as punishments than as treatment.
Chief Bromden is diagnosed as paranoid, although he really seems to see things more clearly than anyone else on the ward, even McMurphy. The Chief does show some features of mental illness, however. He often sees things in a fog, and has trouble feeling emotionally connected to disturbing events at first. He begins the novel unable to laugh, smile, or remember much of his past, and he has very disturbing dreams. His watchfulness, however, makes him a good rather than an unreliable narrator, despite his mental problems.
Chief Bromden says that the hospital is not a place to make people saner, but to encourage people to conform and to fit into an insane world, which he calls the Combine. This is like a machine making whole grains into wheat on a farm. Bromden's first encounters with Randle McMurphy are key steps in his path back to sanity and regaining a sense of himself as an autonomous person, rather than as a subject of the Combine. For example, McMurphy is the first inmate to understand that the Chief is not really deaf, and when McMurphy brushes his teeth with soap, in defiance of ward...
Later, for the first time the Chief realizes that he has free will when he votes for McMurphy's suggestion that the ward should watch baseball on TV. When McMurphy begins to arrange a fishing trip for the ward, Bromden suddenly remembers why he has chosen to assume a cover of deafness and dumbness -- when his tribe's land was being sold from under him as a boy, the white men that came acted as though he had not spoken a word. He finally speaks for the first time in years when McMurphy offers him a piece of gum.
Although McMurphy's defiance is a key element in Bromden's healing, towards the end of the novel Bromden emerges as having more integrity than his 'teacher.' He refuses to accept the money McMurphy wins after winning a bet that the Chief can move the control panel, because the bet was rigged -- McMurphy already knew that the towering Chief could do so. Towards the end of the novel, Chief Bromden appears to be growing stronger, as he is able to mentally retain a sense of sanity even during electroshock treatments. When McMurphy is lobotomized after he physically attacks Nurse Ratched, the Chief is the man who frees McMurphy by taking his life, and escapes the ward by breaking the ward's window with a control panel, and hitching his own ride to sanity and freedom.
