Rob Gronkowski, the NFL star with four Super Bowl rings, made a significant investment in Apple stock at age 25, guided by his contractor's advice. Initially investing $69,000 in 2014, he later cashed out when the value reached $250,000, and now his shares are worth over $600,000, showcasing his financial discipline and foresight. Gronkowski has lived off endorsement money, saving his NFL earnings to secure his financial future post-football.