Thog is one of the Hell-Lords created from the energy released by the battle between Demogorge and the Elder Gods. He came to rule a nether realm known as Sominus, which was the dark reflection of the benevolent yet enigmatic Therea ruled by the god-dogs Zokk and Maftra. There may be a familial relationship to the monstrous Thaug and Thog who existed circa 10,000 B.C. According to some sources, Thog is one of the Hell-Lords who pooled their resources to create a Son of Satan, resulting in Hellstorm and later Satana. In the modern era, the young Jennifer Kale used the Tome of Zhered-Na to play at summoning a demon, bringing Thog to Earth until he was driven back by the Man-Thing.

Soon after, Thog summoned the Man-Thing and Jennifer Kale's family to Sominus, restoring the Man-Thing to human form and offering to make it permanent if he would kill the Kales, but the Man-Thing disintegrated Thog instead. Recovering, Thog used the Tome of Zhered-Na and sent his demons to possess people on Earth, causing mass violence until Jennifer and the Man-Thing disrupted the spell with the aid of Dakimh the Enchanter. Thog then posed as the human Overmaster, joining forces with the Congress of Realities in an effort to merge all dimensions into a single realm; this disruption of the nexus of reality sent Howard of Duckworld and Korrek, warrior of Katharta, to Earth. Ultimately, Thog invaded Therea, but was petrified by immersion in its pure waters. Inspired by the Fear Lord Nox, Thog then used a number of Nightmare Boxes - filled with dark emotional energies - in a plot to plunge Earth into madness. However, the Man-Thing and writer Steve Gerber were pulled into a Box, and the presence of rational thought disrupted the delicate balance, foiling the scheme.

Thog next used the ancient Magus Sword to capture those who could oppose his efforts to conquer Earth, but writer Chris Claremont, briefly transformed into the Man-Thing, destroyed him once again. Thog was one of the Hell-Lords whom Olympian god Pluto allied with in a plot against Zeus, and he also worked with the Hell-Lords in using the Six-Fingered Hand to nearly merge Hell and Earth. Thog later joined the other Lords of the Splinter Realms against the magical entity unwittingly created by Magik (Amanda Sefton) via a computer program to gather magical lore.