You are Maoh. Ruler of the Underworld. You are the source of all evil in this world. You are the grand lord of all demons!
— Tonchiki reminds Maoh of who he is (Go! Greenman)
Maoh's Japanese name Maō (魔王) comes from the combination of the kanji ma (魔), meaning devil or demon and ō (王), meaning king. Therefore, Maoh's literal name is "Devil King," which is fitting due to the fact that in Go! Greenman he is stated to be the grand lord of all demons. Maoh's name is also the Japanese word for archenemy or archnemesis, which fits his persona and role in the series.
According to the Toho Special Effects All Monster Encyclopedia, when Maoh transports himself to the surface world, he is referred to as Avatar Maoh (分身魔王 Bunshin Maō, lit. Avatar Devil King)
Maoh's skin is a dark brown color, which fades in to a nearly black shade on certain parts of his body. His face is located below his arms, in the central portion of his body. In the overworld, Maoh's eyes are a dark brown color and he sometimes appears to have no eyes. However, in the Underground Cave his eyes glow bright red. He has a wide unopenable mouth with several sharp teeth, as well as two fangs which extend from his upper mouth past his lower lip. Maoh also has a large crown of curved spines and a membrane which stretches from his inner arms to the sides of his upper thighs. Maoh's legs are covered in scales and end in large clawed feet.
Maoh is a being of pure evil, hellbent on killing and harvesting the blood of young children in a scheme to escape his imprisonment from the Underground Cave. He is also seen to hold on to intense rage, often taking it out on Tonchiki both verbally and physically, or creating displays of lightning with his hands. However, although seeming unable to feel any emotion beside hatred, Maoh is actually seen showing emotion toward his subordinates. In Greenman vs. Tonchiki, Maoh breaks down in to tears for the then deceased monsters Gabara, Megahertz, King Takoras, Stock, Valingar, Gyaron, and Danbaraki. Furthermore, In Greenman vs. Maoh, after all of the Minions of Maoh are killed by Greenman, Maoh angrily says to the mechanical hero "How dare you destroy all of my darling little subordinates one after the other!" Both instances clearly display Maoh's care for his minions despite his inherently evil nature.
Maoh was the fifty-third, and final, kaiju to battle Greenman. He is the source of all evil in the world, and was banished to an underground cave by God himself to distance him from the humans. To be freed from the underground prison, Maoh must collect the blood of human children. However, his plans usually devolve into pure mischief and attempts to stop his arch-enemy Greenman. Maoh has a loyal underling named Tonchiki, and clay doll servants known only as the "Minions of Maoh" who are tasked with collecting childrens' blood for their master.
Maoh is first seen in Episode 1, "Greenman vs. Garamedon." He appears to suffer from amnesia after being banished to an underground cave which prompts Tonchiki to remind him of his identity, and what he must accomplish to be freed from his imprison, and soon returns to his scheming ways. Under Maoh's command, Tonchiki and one of the devil king's minions attack a group of children at a playground in a scheme to collect their blood. However, an unknown hero stops them before revealing himself as Greenman, a self-proclaimed envoy of God. After a short battle, Tonchiki mutates the minion in to a monster and thus begins a continuous cycle of creating monsters to destroy Greenman. After all but one of the transformable minions are destroyed by Greenman, Maoh teleports to the surface to collect the blood himself, but is unable to move his legs due to his banishment. Using a magic spell, Maoh transforms a group of children into stone, and orders Tonchiki to haul the stone children to the Underground Cave. Greenman then appears and engages Maoh in battle, with Maoh quickly retaliating with dark magic to stop Greenman in his tracks. The remaining children use their Green Calls to free Greenman from the magic and fully recharge his power. Once revitalized, Greenman transports himself to the Underground Cave and grabs the stones before returning to the Overworld. He then uses his Greenman Stick to return the children to their human forms, and teleports once more to the cave to kill Maoh once and for all. He does so through the use of his Flash Shock ability, which immediately kills Maoh and sets the cave ablaze, destroying it.
Maoh can place energy into clay dolls and turn them into his minions.
Maoh can create lightning from his hands, typically when he is extremely angered.
Maoh uses a special incantation for multiple purposes, usually to create or manipulate objects. Once such example of this is when Maoh grants Hotter with a steel sword in Greenman vs. Hotter.
Maoh can teleport out of the Underground Cave despite the fact that he is banished there, however, he can not move his legs when outside.
When Greenman touches Maoh, he can use magic to incapacitate the hero. However, this is not shown to work on mortals, as three young boys punch and kick Maoh with no sustained harm.
Maoh can create severe earthquakes.
Maoh can become invisible by creating a wall of magic, which keeps everything behind it visible except for himself. This smokescreen of sorts is easily disrupted however, as Greenman destroys it using but a single Ear Boomerang.
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