> That article in turn puts forth a surprisingly thoughtful methodology:
https://money.com/richest-people-of-all-time-methodology/.
Here's what this article says about Mansa Musa. First, very few reliable sources for how rich he was:
> Just how rich was Musa? There’s really no way to put an accurate number on his wealth. Records are scarce, if non-existent, and contemporary sources describe the king’s riches in terms that are impossible for the time.
It then quotes a professor who uses an image from a European map of Mansa Musa created 4 decades after he was born as evidence that he was the richest person of all time.
This is the issue. We have a few second hand accounts around the time of his Hajj saying the Hajj was immensely large and luxurious, and it appears that his reign appears to have coincided with a relative high point for the Mali Empire. That's about it, and it's not nearly enough to say he was the richest person in history, or even that he was the richest leader of the Mali Empire. It's worth noting how little we actually know of the Mali Empire - historians don't even agree about what it's capital was.
I looked into it a couple of years ago, and there was no evidence I could find that he was richer than, say, Mansa Sulayman who lead the empire a few years later. Many people seem to consider the Songhai Empire at its peak richer and stronger than the Malian Empire was. Even if we restrict ourselves to medieval West African polities, it's far from clear that he was the richest.
And considering we're looking at West Africa, another problem arises. A lot of people seem to imagine this wealth as being the amount of gold that gold rich Western African polities had times the value of gold if it suddenly all appeared in the gold poor Mediterranean. But this ignores the fact that getting gold there was a difficult task involving skilled intermediaries. Likewise, salt came down from the Mediterranean to the salt poor Mali Empire, where it fetched a large amount of gold. But I don't think anyone would claim that it would make sense to calculate wealth by seeing how much salt a Mediterranean polity had, and then multiplying that by how much gold you could get to it and the end of trade lines in Mali.