???
The inspiration?
Originator, patron, prime mover, ancestor, author.
Casey1505. I thought about having a movement about an hour ago. I did, and it was everything I thought it would be. You should have seen it.
I’ve often heard it as the “father” of the movement.
Progenitor
Progenitrix
“spiritual father”, “intellectual father” , or “conceptual father” is what I’ve heard most.
His work gets described as seminal.
You could also go for precursor, forerunner, harbinger, or anticipator.
Person or persons responsible?
Defendant?
The decedent? That’s after the BATF gets involved.
Cecil, of course! 
Guru?
Tyler Durden.