Well if we're strictly talking about self made income then Gates and the other top forbes list will be in it. But if we're talking about juat plain old cold cash and asset then i would guess the saudi princes and sultans with oil fields to their names. Rothschild and other conspiracy theory families and corrupt officials.
Gates may not be comparable to Arab princes or sultans with all their assets, imagine many countries such as America and Russia are fighting over Arab territories because they are rich in oil, how rich Arab princes have that assets, even if you look at their lifestyle, it's very glamorous with thousands their luxury cars are carved