REUTERS/Steve Nesius Tesla CEO Elon Musk's personal wealth gained nearly $8 billion Monday as the stock surged 11% to an all-time high. Musk is now the fourth-richest person in the world, according to the Bloomberg Billionaires Index. Overall, Musk's net worth has grown by $57.2 billion this year, the second-largest gain behind Jeff Bezos' $73 billion increase. Read more: Bruce Fraser outperformed the S&P 500 by nearly 286% as a hedge-fund manager before switching to real-estate investing.