One
If this is an essay type question, then you might want to consider Bill Clinton. If ever there was a difficult man to judge, it certainly would have been Clinton. I don't have any trouble, because Clinton the man was a different critter than Clinton the leader. Yes he was corrupt as a person. He had flaws and he misused his power. But he was also a president, and in the opinion of many, one of the better ones in the latter half of the 20th century.
Consider the things he accomplished as president.
He was the last president on record who tried to balance the budget. That today is an absolutely positive thing to say about any politician. The debt currently (Federal) is about 60000 US dollars owed by every man woman and child living in America today. Trust me, it wasn't Clinton who added to it.
He kept America out of any major conflict. That too is a major plus. The middle east is a cesspool of involvement. Afghanistan broke Russia and their involvement there resulted in nothing but defeat and humiliation and tears and might have been the cause of their downfall. They had to get out of that barbaric relic. Did Clinton notice? Undoubtedly he did. The man was a Rhodes scholar. Those awards are not handed out in Cheerios boxes.
He did not neglect America's need for social security. He tried to improve medicare and medicaid so these two entitlements would not break the piggy bank. He asked Hillary to spend 2 years of her life trying to rewrite Medicare. He could not help that those who could vote on such thing thought more about re-election than they did about the good of America. Say what you like about the presidents who followed him, but those problems were not their concern. It was his.
We expect our leaders to be virtuous, but that's because the media makes such a fuss about virtue. If you will excuse me for being blunt, sex is much easier to understand than is Afghanistan or balanced budgets. I would be willing to bet that most people can't point to Afghanistan on a map even now. Can you? Can your friends? But you and your grandchildren will be the ones that will be held at ransom for the payments of that involvement and it will not be cheap. It isn't cheap now, let alone later.
Printing Press
I once watched a documentary on the history channel about the 100 most important events in Human History. Of course it was speculation, but it was very interesting speculation. Being a science major, I watched it right to the very end because I wanted to see whether it would be Newton or Einstein who would be considered 1 and 2 respectfully. It was neither. They came 2 and 3.
It was the printing press that came first.
It had so many positive results.
It put the Bible in everyone's hands. That loosened the grip of the Catholic Church on people's lives. The Protestant reformation was one of the three or four most important events in human history and development. The war between Catholics and Protestants is still going on, or there is at least religious strife. But putting the Bible in everyone's hands made it possible for the Protestant tenant of a direct pipeline to God possible.
The printing press made it possible to record discoveries of every nature. Think of how much easier it was for Universities to find out what current scientific thought was. Mathematics for example did not require the person who developed the theory to explain it: his book would (that of course came a bit later).
The Printing Press allowed duplication to become much easier. A monk spending his entire life on one manuscript was no longer necessary.
Keep on in this vein.