This question is going to generate lots of answers. However, in my opinion, Barack Obama has and will leave the most important legacy. The reason for this is because race matters.
Barak Obama is the first African-American president. This alone is an amazing fact, especially in view of America's past history of slavery and many generations of racism. The fact that we have an African American president shows that America is the land of opportunity. Furthermore, it shows that change is possible.
It also says that this we are moving past some of the racism that has characterized us. Most importantly, this fact shows the way forward as well. One of the reasons why American became great was because it embraced all different types of people. If we are going to rise again, it will be through the same way.