The subject of this article or section originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
He is not from the works of J.R.R. Tolkien.
Zog was a skilled Orc from the Mystic tribe and loyal servant of the Dark Lord Sauron. An ambitious leader, he and a group of acolytes went to Gorgoroth to call Tar Goroth, an ancient Balrog who had served as a general in Morgoth's army, back to life and recruit him. Despite the attempts made by Talion and Celebrimbor, Tar Goroth returned, but proved himself to be a foe both to the Free Peoples of Middle-earth and the Orcs.
His success made him even more ambitious and furthered his lust for power, such that he made his own plans to betray and contest Sauron. Using his sorcery, Zog managed to bring some of Morgoth's followers back to life, building his own army of undead Orcs. After Tar Goroth's defeat at Seregost, Zog and his acolytes went there and attempted to raise the Balrog through a ritual. It was there that the sorcerer revealed his new agenda, to submit Tar Goroth to his will and supplant Sauron. Talion slew him and destroyed the totems, ensuring that the fiery demon remained under the lake.
In Minas Morgul, Zog was called back to life by his acolytes, and they began to replenish his army, but Celebrimbor again came against the necromancer, slaying Zog and all his minions. Carnán, in the form of a fire-drake, burned his remains to ensure he could not resurrect.