Influence isn't always a good thing. Hitler is a prime example of that. It'd be a "1" if we're talking about personality; he is probably the most despicable being to ever live, and I hope this world never sees anything worse than this. Unfortunately, Hitler's insanity was multiplied by how much power he had. He managed to convince pretty much an entire country that entire groups of peope had to be killed because they weren't like them. He is the responsible for the murders of millions upon millions of Jewish, Polish, Roman Catholics, Protestants, Romanies, Jehovah's Witnesses, trade unionists, physically handicapped and mentally handicapped people, on top of the people that just didn't like his politics. By the end of the war he created, over 45 million Europeans have died. That's a pretty significant chunk of the human population wiped out just because some guy was a blazing lunatic. Because of the number of people who died, it is impossible to know exactly how much he altered history: he stopped over 45 million people from living their lives and possibly changing the course of history. He could have killed people who would have cured cancer, perfected some type of technology, but there's no way that we can ever know. So, sadly, this is his influence. We'll never know the extent of damage he's done. As Ridge pointed out, genocide was and is a problem all over the world. Their limitation is the amount of power these psychos have. Let's hope that none of these nuts ever get the kind of following Hitler had.

UPDATE:  Wow, it's hard to believe that this psycho still has a fan club out there.  Makes me vomit a little to read the words "he is by far one of the greatest person this world has ever seen" written next to his name.  Greatness isn't defined by what kind of power you have, but what you choose to do with it.