In order to be controversial a person has to have admirers and detractors. A controversial person must be both loved and hated. So, we have to ask ourselves what public figure has had the greatest mix of emotions attached to them.
There are many people who might qualify. For example, George W. Bush was certainly very controversial. Conservatives loved him and liberals hated him. The same was true of Ronald Reagan.
However, I will have to argue that Abraham Lincoln was the most controversial figure in US history. He had people who loved him (mostly in the North) and people who hated him and thought he was the ruin of the nation. Unlike the other two I mentioned, though, Lincoln was controversial enough that his election was the last straw that caused the Civil War to happen. That is surely the most drastic result that has come from any controversial figure in US history.