Complex sentence: Now Makhmudov is the main owner of Uralskaya Gorno-Metallurgicheskaya Kompaniya (UGMK) Holding that is the fourth largest non-ferrous metallurgical company in Russia, Russia's second-largest copper producer in terms of output.
Split into simpler sentences: Now Makhmudov is the main owner of Uralskaya Gorno-Metallurgicheskaya Kompaniya (UGMK) Holding. This is the fourth largest non-ferrous metallurgical company in Russia, Russia's second-largest copper producer in terms of output.