While in Unity, clicking Assets - Import Package - Character Controller results in the folder being empty?
You probably accidentally deleted the contents of it, or Unity didn't install right. Try reinstalling. I'd upload the contents of the folder, but I am not sure if that's legal...
Can you try and see if it will let you re-download it. Windows -> Asset Store -> Login -> click on the download icon at the top, looks like a box with an arrow pointing down. See if you can locate the Character Controller in there, it may just say "Import" but perhaps it will see that the unitypackage is messed up and allow a re-download, just something to try. I can't find the character controller listed on the store perhaps it's recognized just from the installation. Go and check out C:\Program Files (x86)\Unity\Editor\Standard Packages if you are using windows and see if the Character Controller.unitypackage is 0 bytes. That is suppose to be were import comes from. Mileage will vary if on a Mac of course.
Is the "Character Controller" asset the same thing as the "Character" asset? I don't see the exact words "Character Controller." In fact, when I try to search it in the project menu/bar thingymabob, nothing pops up! Why is this so?