Which Terrible Character Had All The Ingredients Of Greatness?

Sometimes, a character fails because they're just not a good idea... but sometimes, a character is a great idea, and they just fail to achieve any of their potential. Which character had all of the ingredients for greatness, but just completely failed to activate them?

Please include a picture or clip showing your chosen character. And please mention his/her name, and what possible makings of greatness failed to come together.

Top image: Jubilee wallpaper, art by Dustin Weaver. She's a homeless Asian-American teenager with the power to detonate matter at the atomic level, and she's besties with Wolverine. She really should have been great.