A tribute to Jack Bogle, founder and retired CEO of The Vanguard Group, is displayed on the bell balcony over the trading floor of the New York Stock Exchange in New York, January 17, 2019. Brendan McDermid | Reuters

Jack Bogle needed hefty amounts of brainpower and market know-how to put together the first index fund. But for investors wanting to cash in on his idea, it's become pretty easy. In 1975, the founder of Vanguard Group, who died Wednesday, was able to turn a long-held belief into reality, namely that it was far more profitable to follow the market than fight it. Most mutual fund managers who picked stocks couldn't keep up with basic benchmarks like the S&P 500, much less beat them, he found. So he turned his thoughts into action, putting together the first fund that simply followed the S&P 500, minus a small management cost that was much cheaper than the active funds of the day.

"When I founded Vanguard, I never sought to leave a legacy as such," Bogle wrote in his final book, published in 2018, titled "Stay the Course: The Story of Vanguard and the Index Revolution." "My goal was to create only an enterprise that was of the shareholder, by the shareholder, and for the shareholder." That one invention, the First Index Investment Trust, has spawned a massive industry that rules investing today. Bogle's passive fund has only a relative handful of peers in the mutual fund space, but exchange-traded funds, of which he was suspicious, have brought index investing into the mainstream. The ETF industry now boasts 1,977 funds, with $3.57 trillion in assets. Most are set up to track indexes.

Three choices