There are at least three reasons why President Eisenhower was considered a true hero by many Americans.
First, he was the American most connected to winning WWII in Europe. While there, Eisenhower had to deal with the political complications of working with the French and British and Russians while also trying to manage the war as effectively as possible. The fact that he was in charge of a successful war made him look very good in the eyes of the people.
Second, he was a successful president. It is true that he was not flashy in any way. However, he did accomplish some important things like getting the interstate highway system going and ending the Korean War. He did not commit any major blunders or get involved in any scandals.
Finally, Eisenhower accomplished all of these things while seeming like a very average American. He was not from a rich or an important family. He was from "Middle America." In these ways, he was the embodiment of what America was supposed to stand for. He was a regular American who did his duty in tough circumstances and did it well. This made him a hero to many.