It was created years ago by a psychologist who tried to eliminate fear. Instead, all he did was externalize it, creating a violent, destructive, creature that lashes out at anything that threatens it.
Occasionaly, twice, and under mental control of a Marine pilot, he has been turned into a force for good, even becoming a member of the Honor Guard.
It appears out of nowhere. It's drawn to the superpowered beings that have so often contained it. It leeches off our energy so that it cannot be harm. Everytime is hit its opponent becomes weaker.
Affortunately it is dependably stupid.