He was akin to a molotov cocktail they could toss at any oppressed populace in europe and have non small odds of civil war. It might be more fair to say they controlled him the same way an incendiary bomber controls fire.

he accomplished their aims, however, and that is enough.

You're right, a genuine activist used by the state for cynical motives is called a Useful Idiot. Ironically, this turn of phrase was traditionally said to be coined by Lenin, although modern scholarship no longer espouses this view.