While last year wasn’t a particularly good year for stock investors, at least one man closed it out with a smile. Ken Griffin, the billionaire founder of the Citadel hedge fund, didn’t just outperform the markets last year – he managed to outperform them by a margin of $16 billion. It was the highest annual profit ever seen by a Wall Street hedge fund, and reflected the 38% return generated by Citadel’s flagship fund. Now we all know that past performance is no guarantee of future gains – but it