America is often referred to as The Land of Opportunity, offering people of all backgrounds and levels of education a chance to succeed and build a fortune through hard work and innovation.

Throughout U.S. history, people have become titans of industry and gained recognition through their accomplishments and industry-disrupting ideas. These figures often rose to prominence by undercutting and outmaneuvering the competition to dominate their industry. Names like Rockefeller, Carnegie, and Astor are still prominently displayed on street addresses, performance centers, and municipal buildings because of the indelible impact those people have had on American history and the economy.

Reviewing the industries that these business magnates dominated to obtain their wealth can be an interesting way to map the trajectory of the U.S. economy over time.

Many of the richest Americans of all time made their fortunes at a time when the U.S. was expanding rapidly and building up its infrastructure. During the second half of the 19th century John D. Rockefeller’s oil and Andrew Carnegie’s steel fed America’s voracious appetite to expand. But many Americans also resented the success of the top 1%, branding them as “robber barons” and arguing their fortunes were made on the backs of their employees.

Today a new class of mega-billionaire has made its money through the internet and related technologies. Jeff Bezos is worth more than $150 billion thanks to his e-commerce giant, Amazon. Mark Zuckerberg — one of the 30 richest millennial tech entrepreneurs — created Facebook and became a self-made billionaire at age 23. He was at the time the youngest person to ever do so.

24/7 Wall St. reviewed lists of the wealthiest people in American history, both those living and deceased, to determine the richest Americans of all time. We converted the estimated net worth of those who have passed away into current U.S. dollars. Real-time estimates came from Forbes.

Click here to see the 30 richest Americans of all time