History is full of great thinkers, brilliant military strategies, wise philosophers, ingenious inventors, bold activists, and all sorts of other virtuous people. Of course, being a great person isn't something that happens by accident. You have to have an opportunity to impress, perhaps because your family got an education, or your country was at war (or at peace) at the ideal time, or the key technology that your new business required to function was invented five years before you had your big idea. 

Millions upon millions of marvelous minds have gone to their graves without ever achieving anything significant simply because they were in the wrong place at the wrong time. It's one of the great injustices of history that we'll never know what such people might have done had they happened to be born some other time.

However, what we do know is when many of the great minds we admire were able to excel - and if we know that, we can start to see what factors helped facilitate their rise to greatness. As they say, cometh the hour, cometh the man (or woman). So we'll give you the man (or woman), and you tell us in which hour - or year, or period - they came!