This kind of stuff is completely subjective. How do you define wealth for autocratic and theocratic leaders? For example, included in the figures for Augustus are almost certainly the entire Egyptian grain trade, which he "owned" only because his armies defeated the native Egyptian dynasty. That's not really a fair estimate of his actual wealth as an individual. Similar problems can be found for other supposedly wealthy leaders - Genghis Khan, any of the Chinese Emperors, Mansa Musa, so on and so forth. It's just difficult to separate the wealth of the individual from the wealth of the state those leaders controlled, because at some point, what you really end up asking is "which ruler controlled the largest share of the largest state", if that makes sense. But that's not the only problem.

How do you define the differences in currency and time? There are multiple methods, all of which are problematic. You could argue that if someone was worth a certain percentage of a certain area's economy or wealth (which is rarely completely objectively determined for lack of good records), then you can equate that percentage for the same percentage of today's corresponding territory. So, for example, William the Conqueror and some of his deputies had vast wealth because they, well, conquered Britain. Britain today is a very rich nation (for reasons that occurred much, much later in British history), so if you assume that William the Conqueror owned X% of Britain now, like he did then, then he'd be worth [insert astronomical sum here]. But there is no good reason to do that. Britain was a comparative back water when William took over, certainly not the economic powerhouse that resulted from being the first nation to industrialize. Similar problems exist for other leaders. Alternatively, you could try and see how much money a person had, compare the price of a common basket of goods at the time of the individual in question and today and extrapolate. But that won't account for the differing prices of goods thanks to a more modern production methods. Most people don't bake bread anymore, they buy it. So there are going to be a lot of assumptions in creating that basket and determining equivalences. Pretty much any method you use will have both positives and negatives and none of them will prove definitively who was the "richest" person of all time because none of them will completely agree.