The Moving Spirit

The good news: this idiom has nothing to do with ghosts

Meaning
The moving spirit is the person who came up with an idea. What sense the idiom is taken in depends on how good the idea is.

Use in Normal Speech
After a good idea.

"Where's the moving spirit behind Operation Mayfair - he or she is a genius!"

After a bad idea.

"OK, guys, who's the moving spirit behind this non-starter of an idea? I have a bone to pick."