Others were born into money.
To find the wealthiest people in the world, Wealth-X looked at its database of dossiers on more than 110,000 ultra-high-net-worth people and used a proprietary valuation model that takes into account each person's assets, then adjusts estimated net worth to account for currency-exchange rates, local taxes, savings rates, investment performance, and other factors. We narrowed that list down to just the billionaires who inherited at least part of their wealth.
Some built upon their inherited fortune to create companies that far exceed those of their parents or spouses - like the Koch Brothers or L'Oreal's Liliane Bettencourt - while others, such as the Mars siblings, haven't actively expanded the family business.
Here are the 16 richest heirs and heiresses in the world.