Previously , `` Forbes '' magazine listed him as one of the richest men in the world , with an estimated net worth in 2011 of , which ranked him 10th in its 2012 list of billionaires -- making him the oldest billionaire in the Top 20 list .
Previously , Forbes listed him as one of richest men in the world , with an estimated net worth in 2011 of US$ 25.4 billion . That made him 10th in the 2012 Forbes list of billionaires .