Tim Cook's fortune is tied to Apple's performance in the stock market.<br />In 2013, two years after Cook became CEO, Apple updated his compensation plan to include large chunks of stock that would vest if, over a three year period, Apple outperformed two-thirds of the S&P 500, an index tracking 500 of the biggest public U.S. companies.<br />Apple is up 31% in the last 12 months, and it's outperformed 81% of the stocks in the index, according to reports from Bloomberg and CNBC. <br />