While serfing the 'Net searching for the answer to the question I found pretty numerous ideas deserving special attention. First of all, some add him to social disturbers. By the way, the Big Nurse herself is in search of every possible cause to send him to the Disturbers ward. Well, frankly speaking, McMurphy is a disturber in a positive sence of the word. I mean he belong to that kind of people who gets sick of inactivity. That's why he bursts into long-established environment and intentionally destroys it. Of course, those who inhabit this atmosphere are woken up by his energy and they don't like it. That's why they consider him dangerous and excentric and new. It's the latter that they mostly afraid of.
Another opinion bases on the concept of Jesus (http://www.bookrags.com/essay-2005/2/18/24539/9666). Some people compare McMurphy with the Christ. As for me, such belief is rather superfluous. First of all, I have never met any prototype of Jesus Christ in American literature (unlike in Russian one. We all remeber Ieshua in Bulgakov's 'Master and Margaret'). Secondly, McMurphy is intentionally striving for better conditions on the ward. I mean his ultimate goal is not to make the Acutes and Chronics' life easier at hospital. He does everything contrary to the Nurse's orders. He contradicts her just out of the wish to contradict, the wish to change. I don't think he cares much about the patients. They are just 'flesh' which are likely to give him support. Jesus, on the contrary, didn't waste his energy on those who were in power. He knew it was useless. I doubt if he was thinking aabout it at all.
Another group of people stick to the opinion that McMurphy is an outsider. Somebody with boisterous personality, first widely accepted and then totally damaged by public unruffled equnimity. I have to disagree with them. The point is that a typical outsider does his best to move away from all other types of people. He himself choses to be alone, abandoned, secluded or whatsoever. As you can understand, McMurphy on the contrary penetrates into the new company in order "to defeat the enemy from the inside".
From my personal point of view, McMurphy can be ranked among outstanding egotists, the prominent conquerors, scientists, kings and villains. Such people are not stopped by the number of victims of their deeds. They want to prove the whole world that one individual costs and is capable of much more than the whole world.