I’m not suggesting this will work for everyone, or it’s always the right or best method to go about creating influential characters in history, but it’s worked really well for me thus far. My method is a little slow (there’s lots of downtime between steps to let ideas percolate) and it’s rooted in the world’s fundamentals, so I’ll also provide a look at the steps prior to actual character creation (those steps that apply here, at least).
Start with a Modern Image
I never begin work on a new world until I have an idea of what I want it to look like when I’m finished. Usually this stems from a core idea, like the pursuit of perfection or fear of the other, and is used to form the foundation of every society that will exist in the world.
Create a Physical Map
Build the layout of your world. Put together a map of mountains, rivers, forests, valleys, islands, continents, deserts, and all manner of formations. Consider climate, ocean currents, and all the other tedious details (and handwave what you don’t want to emphasize in this world). I often create the geography and later explain how it came to be, but it’s more of a mixed process.
Create a Political Map
Given the physical boundaries depicted in the geographical map, create the political/societal layout. Countries don’t need to be constrained by a mountain range, a river, or a sea. Country borders often move over time and for various reasons. Want an island near one coast to be a territory of a country somewhere else? Go ahead. Figure out how that came to be later on, during the history.
Baseline the Modern Societies
For each region/country you’ve outlined in your political map, devise the basics of the modern society. Do they have technology, and how much? What are the major food sources? Mineral resources? What don’t they have access to? What do they have that could be traded away? What is the major religion, if any? What political movements are there? What role does the military play in daily life? Etc.
Baseline the Old Societies
For each region/country, devise the basics of the original society (original here meaning the point in time where you want to start worrying about it). Were the people primarily hunter/gatherers? Did they have a nomadic lifestyle and traveled far and wide, or did they settle in a crossroads of several season species? Did they arrive from space and lose their history, or remember it in everything they do? Etc.
Develop the History
Here’s where things get tricky. Begin writing a region/country’s history in a natural progression from the old society. Let neighboring old societies interact with each other. Explore how these cultures work together or against one another. There’s really no way to abstract this to a general rule; do what feels right to you for the old societies you’ve created. Feel free to tweak the old societies to get the interaction you want.
Create Key Moments
Write key moments into your history. This can be the first time two specific societies interact, whether they are opposed to each other’s views, have much in common, aren’t concerned one way or the other, etc.; a calamity such as an earthquake or financial collapse; a new, revolutionary invention, such as steel; or any other turning point in the way the society would function.
Let each key moment in history be defined by either a major event or a critical figure. Often, major events imply the involvement of a critical figure. These critical figures will be the focus around which your society will shift towards the modern society you’ve previously defined.
Build on What You Have
Going a little further, you can flesh out your critical figures by examining the society they emerged in at the time they emerged. A critical figure will represent a) the ideal of the society as it is; b) the society as a major group thinks it should be; or c) the opposite of what the society should be. Use the society as a lens through which to define the critical figure.