After Atum defeated the Elder Gods as Demogorge in the distant past, a great quantity of evil energy was left behind. That energy eventually dispersed and gave birth to many demons, including Thog as well as Satannish and Mephisto.
2000 years ago, Mephisto, noticing Zarathos' expanionist campaign, criticized Thog, Satan, and Satannish for not taking note of this.
Jennifer Kale, before becoming the sorceress she is today, borrowed/stole her grandfather, Joshua's, Tome of Zhered-Na (or a version of it), and decided to have some fun by summoning a demon. A bat-like creature came through the portal she created, and it chased her until the Man-Thing destroyed it. However, a demon calling itself the Netherspawn rose from its ashes and attacked the Man-Thing. The demon nearly destroyed the Man-Thing until it was able to make its way back to the swamp and was replenished. As the Man-Thing battled Thog anew, Andy Kale set the Tome on fire, which consumed Thog's power as well. The Man-Thing grabbed Thog, who just this once didn't burn, although he was clearly terrified. Instead, Thog's life force was drained into the swamp creature, until Thog was eventually pulled back through the portal to Sominus.
First calling himself "Thog", the Netherspawn summoned the Man-Thing (and the Kales) to a realm via a portal created by Jaxon (a former boyfriend of Jennifer Kale who had been mutated by a demon sent to the swamp). The Man-Thing was returned to the form and mind of Ted Sallis, and tempted with a variety of worldly pleasures. Thog offered to allow Sallis to remain in that form if he would kill the Kales. Sallis, refusing to kill anyone, forced himself to return to the form of the Man-Thing. Thog attempted to use his power to incinerate the Man-Thing, but apparently was disintegrated himself.
Thog and the demons of Sominus began to takeover the minds and souls of a number of people, prompting acts of madness and violence across the world. Joshua Kale summoned the Cult of Zhered-Na to oppose Thog, but the sorcerer Dakimh teleported Jennifer Kale and the Man-thing to Sandt to test them for future use against Thog's forces. After proving their worth, Dakimh brought the two to retrieve the original Tome of Zhered-Na to disrupt the demons' spells. Jennifer and the Man-Thing succeeded in disrupting the spell, sending the demons back to Sominus, and restoring (relative) sanity to the Earth.
The Nexus of Realities contained within the Man-Thing's swamp was disrupted by a series of assaults on it, both mystical and mundane. Thog, posing as a human known only as the Overmaster, joined forces with Congress of Realities in an effort to merge all of the Realities into one universe, under his control. Dakimh summoned the Man-Thing, Jennifer Kale, and two victims of the Nexal (brand new adjective!) disruption, Korrek the Barbarian of Katharta, and Howard the Duck, to oppose Thog. The five opposed Thog's forces and the warriors of the Congress of Realities as they began their invasion via the Man-Thing's swamp. They then traveled to the realm of Therea, the dimensional opposite of the demon-realm of Sominus. Therea was the last place untouched by the invasion of the alternate realities, and the site from which they planned to reverse the merging of the dimensions. The Overmaster, revealing himself as Thog, led his allies to Therea and attempted to stop Dakimh and his allies. This time, Thog held his own against the Man-Thing, until their struggle brought them near the moat of the castle in Therea. The purity of the water of Therea had the potential to destroy Thog. Thog was filled with terror of the water, and burst into flames while struggling with the Man-Thing. Thog finally tore himself free, but his own momentum carried him into the moat, where he was carbonized, or petrified, or something-elsed gray and immobile.
Shortly after escaping his imprisonment in Therea and returning to Sominus, Thog was presented with the Nightmare Box by some of his servants. Thog was allied with Klonus and Mortak in this endeavor.
Thog used the Magus Sword of Captain Fate, which had been given to John Daltry, to take control of Daltry. Thog used Daltry (and the sword) to capture a number of Earth's sorcerers, including Clea and Dr. Strange, Jennifer and Joshua Kale, Jimaine and Margali Szardos, and...Chris Claremont, and imprison them in Sominus. Using Daltry, Thog had defeated those he thought powerful enough to stop him. Thog planned to kill his prisoners and then take over the Earth, followed by the universe, and probably then the multiverse. An agent or manifestation of Death, John Kowalksi, conferred some of his own power to another human woman, Barbie Bannister, the former lover of Daltry. Kowalski then brought Barbie (and the Man-Thing, naturally) to Sominus to stop Thog. Thog was prepared, and bound Barbie in a crystal pillar. The Man-Thing then attacked Thog, who again transformed the Man-Thing back into Sallis, but the essence of the Man-Thing then was conferred onto...Chris Claremont
The Claremont/Man-Thing confronted Thog, giving Barbie the time to break free of her prison. Thog grabbed Barbie, planning to finish her off, but she turned her death power on him. Thog crumbled under the attack, but summoned the last of his power to generate a bolt of lightning that separated he and Barbie. As Thog threatened to kill Daltry unless Barbie left, the Claremont/Man-Thing assaulted him. Thog attacked the Man-Thing with the power of the Magus sword, however...Thog knew fear and burned at the touch of the Man-Thing, leaving behind only ashes. Dr. Strange switched the Man-thing curse back onto Sallis, but could do no more.
Along with Mephisto, Thog appeared as one of the demons (and possibly Death Gods) with which Pluto was allied in order to coerce Zeus' compliance with the forced marriages of Hercules to Hippolyta and Venus to Ares. However, Zeus eventually withdrew his cooperation when he was convinced that Pluto may have promised the death of Zeus to those demons in order to gain their alliances.
Thog joined with Mephisto, Satan, and Satannish in a plot to take advantage of a series on "injuries" to the fabric of reality to merge their realms of Hell with Earth. The demons agreed to a contest against the Defenders, the winners of which would decide the fate of Earth. Thog led an army of souls who had suffered in various wars against Devil-Slayer, Gargoyle (Isaac Christians), and Nighthawk. Nighthawk convinced the souls to fight Thog's will and not perpetuate further bloodshed. Thog dropped nuclear warheads to kill them all...but since the demon's reality had not yet come fully into phase, no one died. Eventually, Satan, (after defeating his son, Daimon, in single combat), realized that he had love in his heart for the "Son of Satan" and couldn't kill him. Daimon agreed to remain in Hell, and Satan announced that the Defenders had won, defeating him by bringing out the light in his darkness, and so the demons and their servants aborted their plot against Earth.
Thog, none the worse for wear, appeared at a convocation of demon-lords, gathered to unite against an immensely powerful malevolent magical force, inadvertently created by Magik (Amanda Sefton). Thog, and the forces of Sominus, participated in the battle, but Magik destroyed the creature when she destroyed her magical computer program that created it.
Powers / Abilities
Thog can fire bolts of flame or magical energy. He's good at coming back from the dead. He possesses superhuman strength and durability, and some magical ability. Under certain circumstances, he can open interdimensional portals.