As per Google search these are the top 3 richest person of this world.
1.Jeff Bezos $108.9 billion
2.Bill Gates $91.9 billion
3.Warren Buffett $90.1 billion
But these maybe wrong since in this world there are lot of blackmoney is available which were not recorded by any governments.
In my opinion the politicians from the third world countries can be in the richest persons because they were stealing all their country's taxes.
Even if the corrupt politicians from third world country take all the taxes of his government,this cant reach a hundred billion dollars,meaning thats far from reality
But you are right about the unaccounted money some individuals has.and i believe some of this amount are hidden here in cryptocurrency