Hmm. I wonder how Mansa Musa's fortune compares to that of Lucius Annaeus Seneca aka Seneca the Younger, of the Roman Empire.
Seneca, in addition to his more well-known activities as a writer, statesman, imperial advisor, and Philosopher, was also ridiculously wealthy. I remember a philosophy class where the professor telling us that at by the time of his death, he had a fortune of over 600 Million Sestertii, mostly accumulated through usery. That was several times the annual budget of the Roman Empire - easily enough to have wrecked the Roman economy if he'd used it that way. The professor thought it was a greater fraction of the world's actual wealth than ever controlled by any other single person, before or since. But I don't think the philosophy professor was counting Africa.
Seneca's the poster child for predatory lending practices: he gave large loans to the kings and emperors of other lands, secured by collateral worth more than the loans naturally, and would then foreclose without warning at a time when he knew the loans couldn't be repaid, claiming the collateral. If he could manage it he'd wait to pull that stunt until the victim had been already making payments for years and the loan income was about to run out.
He's also reputed to have paved the way for Roman conquest more than a few times by calling in all the loans he'd made in some country at once, so that they could only just barely be repaid, tanking the local economy so they couldn't field a defense just a year or so before the planned invasion. Or deliberately tanking some country's economy like that so that some third-party would overextend its own military budget and drain its resources invading them - then offer a loan to the third-party that didn't realize what had just happened - then a few years later tank *their* economy right before the Romans invaded taking both territories.
And the Roman empire would often pay him hansomly for his help! Especially since he would "advise" the Emperor to do so and often controlled a seat in the Senate and, you know, had connections.
And this guy wrote about Stoicism - accepting your lot in life, as every position has value, every calling is great when greatly pursued, and attempts to better your station cause only strife. Advising slaves to be loyal to their masters, and so forth. While ripping people off left and right.
Boudicca and a few other people got really, really angry with him. Can't blame them a bit actually.