When it comes to the richest person in U.S. history, taking inflation into account, John D. Rockefeller is widely regarded as holding that title. Rockefeller co-founded the Standard Oil Company during the late 19th century, accumulating an immense fortune. When adjusting for inflation, his net worth is estimated to have reached approximately $400 billion, making him one of the wealthiest individuals in modern history. It is important to note that determining the exact ranking of historical individuals' wealth can be challenging due to various factors, such as wealth fluctuations and the complexities of accurately adjusting for inflation across different time periods.