No matter what he does, every person on earth plays a central role in the history of the world. And normally he doesn't know it.

This quote is saying that each and every person in the world has an important role to play in the history of the world, even if they don’t always realize it. Every person plays a part in shaping the world and helping it become what it is today. Every individual has the potential to have a lasting impact on the world, even if they don’t realize it.