That led me back to a discussion I was having with Beth about the people in history who have done the greatest good. How is greatest good defined? Well, it's not easy. Norman Borlaug saved a billion of lives, sure, but he also put a similar number in jeopardy by helping the agricultural system become more monoculturist, which means that he delayed its fall until there were more people depending on it (if it falls -- it hasn't yet.).
I can't find a good read on how many lives DDT saved by effectively ending malaria in much of the world. I do find it amusing, however, that they used to infect syphilis sufferers with malaria so they could use quinine to control their fevers.
But what about other things? Thanks to Gandhi, there's an alternative to violent uprisings. Or should we give the credit to Saad Zaghloul? He was responsible for the Egyptian revolution of 1919, which could be said to be the first major nonviolent resistance movement. Either way, that's saving lives in a very different and much harder to count way.
You could give credit to Buddha for not saving lives, but making them better. Unlike other major religious figures, you don't need to have too much of an argument about the downsides of his philosophy. Similarly, you could give credit to Adam Smith for pointing the way toward our current global economics. Thomas Malthus would be shocked by how many people currently live, so I could see an argument for Adam Smith and David Ricardo in terms of increased quality of life for people. This is definitely in the fuzzy area. Similarly, the invention of sanitation in the forms of sewage removal and treatment, and solid waste removal, would probably classify if they had an inventor.
Lots of people did great things, but it's gotta compare favorably with saving a billion lives to make it onto this list, so think deeply. Still, you probably can't do worse than this list. Who've you got?