well with how dominated society is by technology nowadays, id have to say edison or tesla were quite crucial in our development, this leaves out plenty of names though because technology was more of a group effort, everyone had a piece of the puzzle.
as far as impressions left on humanity, ceasar and genghis kahn were crucial in showing us what man is truly capable of, as well as hitler unfortunately, all were great at influencing nations to do things they probably didnt believe possible in theory, and most understood what it took to rule over large territories while avoiding uprising, even before machiavelli(also another very important person who revealed a lot about human nature and psychology, along with freud), they understood power was more important than being accepted by their people.