How do you choose who the most important people are? From my perspective the way you do it is to pick people that significantly changed history, and it "stuck". By that I mean there is a course to history that generally works itself out - empires are founded, and they fall. Religions rise and fall, and philosophies (communism, socialism, fascism, etc...) rise and fall. However, there were some key people, that without their intervention, the course of history would have turned out significantly different.
- Martin Luther - as I noted in the previous post the genius Martin Luther broke with the Vatican and invented high German as a language. It is true that the hold of Rome over the provinces was going to fall at some point and nationalism was rising, but it was his particular genius to create a reformed church as well as bring it into a format that was understandable to the layman
- George Washington - by refusing to make himself King and standing by the principles of democracy, George Washington changed the course of history. While Britain has long been a democracy, it is overlaid with the royals and so their course is hard for other nations to follow (enlightened royalty is rare indeed). However, the US created a blueprint for democracy that could be followed, although it obviously had flaws (that landed in the lap of the next person, below)
- Abraham Lincoln - Lincoln led a horrendous war to hold the union together and abolish slavery, that compromise that almost fatally ruined the US democracy. He was a magnificent orator and man of incredible strengths - he was able to hold the North together and win bitter elections, as well as lead the military and find commanders like Grant and Sherman who could finally push the war to its conclusion. And at the end of the war he advocated reconciliation, which was sadly cut short by his assassination. It is more than likely that without his towering strength the US might have been cut in two or the Europeans would have meddled in the conflict, leading to unforeseen conclusions. Democracies of continuing strength are terribly rare - look at Europe and South America for comparison
- Winston Churchill - the indomitable Winston Churchill was a genius and a man of ferocious temperament, as well as being an all-time orator at the level of Lincoln. When he returned in 1940 a message went out to the Royal Navy "Winston is Back" that is a classic along the lines of "Nuts" as a response to the German surrender entreaty at the battle of the Bulge in 1944-5. Mr. Churchill was struck by a cab when visiting NYC in the 1930's and I shudder to think of how the world may have turned out without him. Without his indomitable leadership Britain likely would have negotiated a peace with Hitler, leaving him master of the continent, and taking the world down an unknown (and likely horrible) course. Who knows if Hitler, after negotiating with England, might have continued his alliance with Stalin, and split the known world between them?
- Norman Borlaug - after WW2 the population exploded in Asia and starvation was soon to follow, as it always had. But Norman Borlaug intervened and created and led the "Green Revolution", saving perhaps a BILLION lives. The green revolution allowed the food supply to keep up with the population growth and avoid famine (except for areas where poor government allowed it to happen, of course). He is poorly known but that is incredibly unfortunate - Bono and the rest of the Live Aid crew could learn from him, for now he advocates bio-engineered food to feed the poor, while Europe would rather let everyone starve and label them "Frankenfood". Here is a great article about Norman Borlaug, but you need to subscribe to the Atlantic Monthly, something I strongly recommend anyways :)
- Margaret Thatcher - In the 70's England was in decline with the rest of Europe, stumbling down the rat-hole of socialism with crippling union strikes, high taxes, and myriad other blocks against capitalism. Margaret Thatcher stood up to the unions and pushed the reforms that have made Great Britain great again - when you go to London you see a thriving financial capital, full of people from around the world. Unemployment is way down and Britain is a destination of choice for the wealthy who need to escape punitive taxation in their home company. It didn't have to be this way - they could have turned out insular like France or fractured like Italy - but thanks to the reforms that Margaret Thatcher set in motion Britain created their own history. The fact that she was a strong woman also set a precedent that is very valuable in our world, as well
- Deng Xiaoping - purged three times by the Communists, Deng survived and set in motion the reforms (first in the countryside, then in the cities) that loosened the chains on the Chinese people and led to an immense increase in wealth for them and the world. The overseas Chinese always proved to be formidable capitalists (Hong Kong, Taiwan, Singapore, Indonesia and in the US) but now they were freed within their own country. China still has horrendous problems and is not a free country but the changes that he pushed made lives better for hundreds of millions of people and everyone acknowledges China's impact on the world. He changed China by setting free capitalism on a massive scale and turned the course of history
Note that Hitler, Stalin and Napoleon aren't on the list - they all created empires that rose and fell but other than the deaths that they piled up the world is back to where it started, with Russia surrounded by enemies and falling back on authoritarianism, an enfeebled Germany, and an insular France. Mao put the country back together but it wasn't really falling apart - for the most part China was ethnically homogeneous - but he accomplished little else and committed massive atrocities.
Nelson Mandela actually isn't far from making the list - everywhere else in Africa when the whites were pushed from power they were expelled or made to feel so unwelcome that they left on a massive scale - and if he can create a multi-racial society there (even one with big problems) that would be a beacon of hope for Africa and the world as a whole. As a long political prisoner he had an axe to grind if he chose to do it, but he instead did his best to move forward peacefully. His biggest mistake was turning over the country to Mbeki, whose lunatic beliefs that HIV doesn't cause AIDS led to the unnecessary death of millions of his countrymen (note that South Africa, unlike most of the rest of Africa, had a health infrastructure that COULD have blunted the disease, but he chose to do nothing).
Sharon of Israel might yet make this list if he succeeds in pulling out of the indefensible areas of the West Bank and holds the Israeli state together. Of all the military successes in history, Israel is one of the most amazing, since it is surrounded by hostile enemies bent on its destruction. Eventually all of the other military states lost out when they took on their immediate enemies and were outnumbered, but Israel has been able to hold on, breaking the tide of history.
Ghandi would seem like a good choice for a list like this to the relatively informed reader, but in fact India is still very much a work in progress, riven with tremendous ethnic strife and on the knife edge of catastrophe with Pakistan, all of which fell out of the bad border drawing in 1948 and their inability to resolve the outcomes of that partition. All that being said, if India's growth continues and they are able to work things out with Pakistan on Kashmir, whomever does that for India would be on the short list for greatness due to the immense impact of the soon-to-be most populous country in the world.
For scientists, other than Borlaug, it is hard to point to a SINGLE individual that substantially changed the world, with discoveries that wouldn't have otherwise been made in the near term, with the possible exception of Einstein. His theory of relativity is beautiful and I am not enough of an expert to speak with authority, but I think it would have been a long time before someone came up with all of these elements of his theory. He also impacted the world with his letter to Roosevelt on the atom bomb, but likely we would have found it anyways (at some point, but probably not soon enough to end WW2 and save 1 million US casualties from Operation Olympic). He is probably on the edge of this list, I don't know.
Don't like my choices? Pick your own :)