It's hard to sit in 21st century America and grasp how much Edison's signature invention affected the world at the end of the 19th. Beyond the light bulb, though, with his labs at Menlo Park, he developed a method of developing things that was enormously productive. I doubt I need to tell you about Tesla, as there's somewhat of a Tesla Renaissance going on these days. I wouldn't single out William Shockley without the coinventors of the transistor, Walter Brattain and John Bardeen. As I've said before, mankind has made more transistors than any other thing we've ever fabricated, including nails. Charles Richard Drew developed the modern blood banking system, which has improved the lives of billions.
- Thomas Edison
- Nikola Tesla
- William Shockley
- Charles Drew
A very distinguished group. But what about others? First, it's almost inevitable that a list like this will tell you as much about the preparer than the people on it. With three engineers to one doctor, it has a decided technical leaning. Commenter Matthew Wennerlund nominated Norman Borlaug, the agronomist who developed what we call wheat these days (genetically very different from the wheat our ancestors ate). He has undoubtedly saved or enabled the lives of billions of people and in terms of pure numbers it's hard to top that, no matter how wretched that "wheat-like food stuff" is and no matter how many people have problems with celiac or related syndromes from it. That's a "first world problem". If you starve to death in childhood, you don't get celiac later in life. It's similar to how the gene mutations that causes sickle cell anemia survives and isn't selected against: the gene gives survival advantage against malaria, allowing children to live long enough to reproduce.
I think there's a place for the pioneers of rocketry to be considered, such as Konstantin Tsiolkovsky or Robert Goddard, suggested by another commenter. But we should be tying to narrow this down to the single "greatest figure", not just add people.
From my parochial perspective, I'd think of Edwin H. Armstrong. In the earliest days of electronics, Armstrong invented the essential "superheterodyne" architecture used in every type of radio, which is still the way it's usually done today, as well as inventing the FM mode. Everyone who has used radio, TV, cable TV, weather radar, or hundreds of other things, has benefited from Armstrong.
What do you think? Did you notice that not one of these people is a government official? When you go to consider them, you end up looking at the ones who caused the most death and destruction in the world: Hitler, Stalin, Mao... Just goes to show you, when you look for the "Greatest figure", you end up with scientists, engineers and doctors. When you look up the ones who have done the most damage, you get politicians.