ProPublica has the article The Great Inheritors: How Three Families Shielded Their Fortunes From Taxes for Generations.

In the early 1900s some of the wealthiest Americans claimed their fortunes would never last through the generations. A century of tax avoidance later, the dynasties are going strong.

This is a long article which I have not completed reading yet. The part that I have read is enough to give me an idea of how our current wealth inequality was created, and who are the people who created it.