William "Bill" Gross (born 1944) is a highly influential American investor and retired fund manager, widely known as the "Bond King" for his groundbreaking work in fixed-income investing. He co-founded Pacific Investment Management Co. (PIMCO), where he managed the Total Return Fund, which became the world's largest bond fund, at one point controlling nearly $293 billion in assets. Gross was celebrated for his active and often aggressive bond strategies, successfully navigating markets and even advising the Treasury during the 2008 financial crisis, earning him Morningstar's Fund Manager of the Decade in 2010.

Drawing unique insights from his past as a professional blackjack player, he famously applied methods for spreading risk and calculating odds to his investment decisions. Gross left PIMCO in September 2014 to join Janus Capital Group, ultimately retiring from active fund management in 2019, and later publicly shared his Asperger syndrome diagnosis.