Who was the ‘Donbass Cowboy’, the pro-Russian Texan who died in Donetsk?

Russell Bentley, a Texas native better known by his nickname “Donbass Cowboy”, died in mysterious circumstances near Donetsk. His death provoked a strong reaction in Russian ultra-nationalist circles, where Bentley had made a name for himself over the past ten years by travelling through the territories occupied by pro-Russian forces in Ukraine.