Oh, so we're talking about fictional characters?
Great:
- Emperor Palpatine -He just is.
- Dr.Evil - Do I need a reason?
Could Have Been Great:
- Darth Maul - In my opinion, he wasn't explored enough and was killed off far too early.
- Adam Sandler - Once a hero, now turned to a so-so villain because he keeps starring in his own movies.
Endless "Could have been great" Soul