A Random Walk Down Wall Street (Burton Malkiel)

First published in 1973, now in its 13th edition, Burton Malkiel's masterpiece made the academic case for index investing decades before it was mainstream. His "random walk" theory — that stock prices move unpredictably and no analyst can consistently beat the market — enraged Wall Street and liberated individual investors. The book walks through every investment fad from tulip mania to crypto and shows why a diversified portfolio of low-cost index funds beats them all. It's the reason Vanguard exists.