There are lots of attributes that are better covered by either a copyright or trademark, but suppose there is a business that makes movies, short films or games or comics uses and "Darth Vader" in their project (without permission) but visually makes them look very different. Does Lucasfilm's or Disney's (or whoever owns IP for Star Wars) copyrights protect against that usage?
If we were just dealing with an image or just dealing with a name, the answer would be clearer, but Darth Vader or Luke Skywalker or R2D2 (or other SW characters) are overall characters, not just an image nor just a name, but I don't know if it's a necessity that for such a name to be trademarked.