Jack Bogle, 88, has done well for himself. The founder and retired CEO of The Vanguard Group created the very first index fund in 1976 and has accumulated a net worth of somewhere in the low eight figures.

Still, "I really can't stand spending money on myself," he told Reuters in a 2012 interview. "I don't like going into stores, I don't like the whole process of buying things."

His frugality comes from his upbringing. "My father's money vanished in the Great Depression, and he had trouble keeping a job," said Bogle, who started working at age 10, delivering papers. "I learned you work for what you get."