From what I understand their 'person of the year' is someone who has made headlines more often, could be for good or bad reasons but they have hit the headlines I am surprised Netenyahu is not on that list, (maybe next year)
I guess it may be people who have done significant things to changed the world, or a course or path that was being taken, for example I think Stalin in 1939 was neutral, by the time we got to 1942, Hitler had decared war on Russia, who by entering the war, changed the course for the better (at least in terms of the allies)