Final answer:
At the time of his death in 1877, Cornelius Vanderbilt's estate was valued at over $100 million, making him one of the wealthiest individuals in US history.
Step-by-step explanation:
When Commodore Cornelius Vanderbilt died in 1877, the value of his estate was over $100 million. This substantial wealth placed Vanderbilt among the top three wealthiest individuals in American history. His fortune was largely attributed to his vast industrial contributions, particularly in the railroad industry. Vanderbilt was instrumental in consolidating several smaller railroad lines to create the powerful New York Central Railroad Company, significantly impacting the American economy by providing efficient connections from Midwestern suppliers to eastern markets.