Wealth is a bit of an abstract concept that makes difficult to generalise across the entire history of civilization. I don't want to sound all hippy-ish, but what exactly makes something valuable? The value of commodities has shifted ridiculously over time, you will have heard the tales of how salt and spices were once worth their weight in gold.

I can't provide any sources here but, by modern estimates, Mansa Musa I is thought to be the wealthiest person in history. Worth about 400 billion in US dollars, he ruled the Malian empire in East Africa in the early 1300s

At the time, this put him in control of the majority of the world's supply of salt and gold.

First time poster here, but from what I know it was Crassus. He would essentially offer to buy out properties that were on fire for low sums. If the offer was accepted, he would put out the fire and rebuild the property. If the offer was rejected, he would leave the buildings on fire without any help. Also according to the wiki article, after his death the Parthians poured molten gold down his throat to symbolize his thirst for wealth. I am not sure of today's equivalent of his wealth as it is often disputed by historians.