With inherited wealth in the news thanks to Thomas Piketty, it's cool that Bloomberg's billionaires interactive lets you sort billionaires according to whether they're self-made or inheritors.
Except this turns out to be challenging, and Bloomberg seems to err systematically on the side of proclaiming people self-made. Take Charles and David Koch, who inherited a substantial oil company from their father and then built it into an even bigger business. They're both "self-made" according to Bloomberg. But how many of us are lucky enough to inherit an oil company?
They also consider Alwaleed al Saud to be a self-made man. But the "al Saud" here is the ruling dynasty of Saudi Arabia.
At any rate, there's no cut and dry correct answer to this. Among the class of people who inherit a lot of money, the richest will be those who go on to manage their fortunes in a skillful or lucky way.
Another thing we see from the list is the importance of family size. Had Sam Walton had two children, they would be the second-richest and third-richest people on the planet. But instead he had four children, so his heirs currently occupy slots 9, 10, 12, and 13. If the very rich were to consistently maintain above-average levels of fecundity, that would disperse intergenerational wealth accumulation pretty effectively. By contrast, if they decided to adopt primogeniture the heirs would inherit the earth quite quickly.