Jack Bogle was an American investor and the founder of Vanguard Group, a company known for its low-cost mutual funds and index funds. He is credited with popularizing the concept of index investing, which allows investors to buy a broad market index rather than individual stocks. This approach helps reduce costs and risks associated with investing. Bogle was a strong advocate for the average investor, emphasizing the importance of long-term investing and minimizing fees. His philosophy and strategies have had a significant impact on the investment industry, making investing more accessible and affordable for millions of people.