Well, yeah?
Who got the ball rolling? CIA.
Who perfected it? SAS boys behind WatchGuard.
The 90's saw a few outfits pop up here, but then Blackwater came onto the scene around 1996 and they're still around and now on their 3rd name. There's more now, specialized and work for either governments or NGO's.
And until laws are passed to ban their use...everybody uses them. Russia - Wagner. Redut, Slavonic, Fakel, Patriot & ENOT.