In the fourth century, an evil tengu known as the Shredder began to wreck havoc across Japan, planning on dominating the world. The Emperor summoned Japan's greatest warriors, Kon, Juto, Chikara, Hisomi and, the most skilled, Oroku Saki. Armed with mystical armor, the five warriors battled against the tengu Shredder. The fight ended when Saki managed to topple the demon and was poised to finish the job when the demon communicated with Saki on the astral plane, offering him power and the world in exchange for his soul. Immediately, Saki's dark side allowed the Shredder's soul into his own before destroying his empty husk.
The five warriors returned to the Emperor, who declares them the Five Dragons and gave them the "Three-Toed Sign of the Dragon" as their symbol. However, Saki took up the mantle of the Shredder and conquered Japan, inverting the symbol to his own. The other Dragons went around the world, learning ancient arts from mystic masters, until they returned, having transcended mortal boundaries. The four battled against their former comrade in a magical battle, manifesting their worldly avatars. Ultimately, the Shredder was defeated but could not be destroyed, so the Dragons sealed him in a coffin and hid his helmet and gauntlet. They kept watch over these objects, for if they were to be reunited then the Shredder would rise again. To help them preventing his revival, the Dragons declared themselves the Ninja Tribunal and taught their secret art to pure and worthy warriors as their acolytes. Seven hundred years later, however, an Utrom criminal, Ch'rell, took up the mantle of the Shredder as his own, playing on the legend to gain respect.
The Foot Mystics sent a bone demon, hidden by an amulet, to locate the Lap of the Gods and revive the Shredder. But the Turtles were able to see through the cloak and managed to hit the amulet, allowing him to be defeated by the Ancient One and Splinter. The Tribunal then separated the objects.
By the 21st century, the five Foot Mystics broke free of Karai and sought to free their master. When the artifacts were gathered together, they defeated the Tribunal and took the artifacts to New York, where they revived the Shredder so he could take revenge on Karai, who usurped his title. He prowled his way through the Oroku Saki Memorial Library to get to Karai, but she proved resilient with the magic-based weaponry Dr. Chaplin developed. When his helmet fell off, the Shredder's face resembled his living self, which Ch'rell had taken on as his false identity, causing Karai to believe she had struck her master. The Shredder's face then changes to its undead form, and he says mortals are such fun to toy with, clarifying that he was messing with her. He then turning her sword into a snake. He then stripped her of her armor and decided that she would make a fitting slave. But the Turtles' interference forced him to reveal his demon and undead minions he could summon while in the netherworld, turning the top of the tower into a graveyard. His minions had Karai still, and he proceeded to strike her when Chaplin tried to defend her. The Shredder could instantly see that he was in love and decided to cut it short, wounding Karai. The Turtles summoned their dragon avatars to battle the Shredder, sending him and the Mystics plunging down to the ground. As they retreated, the Shredder looked at the modern world and announced his plans to modify it for his own.
Capturing the Mayor's office, the Shredder began to turn it into his citadel with an expanding dome, transforming New York into a world of monsters. But as he required more energy to complete the transformation, the Mystics had made sure that city officials create the keystones in a triangle to amplify the spell. When the Turtles tried to reverse it by using the Keystones' power against Shredder, the Shredder found out and was angry that the Mystics didn't inform him. He prevent the spell from being broken, strengthening it to finish the transformation.
The Turtles, allied with their fellow acolytes, the Purple Dragons, the Earth Protection Force, Justice Force and the Foot Clan, lead an attack on the Shredder. Karai, having taken on the mantle of the Shredder, had a link to sap his energies to weaken him so they could separate the helmet and gauntlet. But as he was rendered unconscious, Hun kicked him to make sure he is dead but the Shredder wakes up and blasts him. He then transport Splinter, the Ancient One and the Turtles outside, where he rode on a demon horse, preparing for the hunt. He strikes down the latter and goes to attack Splinter when Hamato Yoshi manifested from the Turtles' medallions. He snatches the Shredder's trident and then slashes him with it, causing precious energy to leak from his armor. To repair himself, the Shredder restores New York to normal before transforming into a dragon. The Turtles also become dragons and battle against him but the Shredder proves too strong. Karai begins to sap his energy again, so he goes to destroy her. But the Turtles strike back as he slowly gets weak, reverting to his human form. Out of desperation, Saki tried charging against his foes, but they then toss him around, separating his gauntlet, which is crushed in Mikey's mouth, and helmet, which is stomped on by Leo. Then the Turtles return to their normal forms, their acolyte amulets are destroyed and as for Yoshi's spirit manifested once again, he slices the demon in half. In addition to the Shredder's physical form being destroyed, his demon essence was destroyed as well because Yoshi was summoned as a completely astral manifestation, a full projection of purity from the astral plane that can eradicate demonic essences. Therefore, the one true Shredder was utterly vanquished forever.
Back to the Sewer
At some point in the future, the Utrom Shredder, the Original Shredder and the Cyber Shredder, were seen engaged in battle with each other, whilst members of the Foot Clan loyal to the Utrom Shredder and those loyal to the Cyber Shredder were seemingly at war with each other. It's not explained how the Tengu Shredder returned or why none of his Undead Foot Soldiers were present. However, it can be assumed the Shredder wished to fight at maximum power instead of diverting some power to summon his undead minions. It is worthy to note this future did not occur because the principles of time travel suggest this was an alternate future. Raphael commented on how this was a twisted future with three Shredders. It was a possible future, but did not occur.
The Original Shredder is a being of pure evil: His goal is nothing short of total conquest, and he will destroy everything in his path on his way to achieve this aim. The demon has a sadistic sense of humor, seeing everything as a game and toying with his foes by using a mere fraction of his incredible power - however, he becomes much more serious if he comes upon adversaries who could threaten his power.
It should also be noted that even though Oroku Saki allowed the Shredder Tengu to consume him, his personality remained dominant in their new form, although he is clearly being influenced by the demon's soul.
The Original Shredder Tengu
The Tengu Shedder is made of two separate beings: The Shredder Tengu (or Demon Shredder) and Oroku Saki (one of the Five Dragons). According to the Ancient One, no one knows what level of the dark depths spawned him, but back in the year 300 AD in Hamato, the Shredder arose from some foul pit in the form of a Tengu, a demon that had but one goal: subjugate the world and turn it an empire full of agony and destruction. The demon spread his evil everywhere and seemed unstoppable until the five greatest warriors in Japan, led by Oroku Saki stepped forth to oppose him. Oroku Saki dealt the final blow, seemingly have put an end to the demon for good and the five warriors became known as the Five Dragons.
Though it appeared Oroku Saki had defeated the demon, in reality he had struck a deal with the Tengu who promised he would make Saki a god among men by allowing the Tengu's evil spirit to merge with Saki's human soul, and becoming the host to the greatest evil the world had ever known. Oroku Saki's betrayal plunged Japan into an age of darkness, the malevolence of the Shredder flowed within him and all around him. He became the most feared warlord in all of Japan, The Shredder. Only through the combined might of the remaining four Dragons could they defeat their former comrade.
The Demon Shredder is one of the most powerful beings in the TMNT universe, with the ability to remake an entire planet in his own image. He mostly relies on his dark magic in battle, which becomes even stronger as more of the world's mystical ley lines fall under his control. He can fire very powerful dark energy blasts, use telekinesis, control and manipulate the elements, regenerate from injury, summon armies of Tengu (including demons, undead, and assorted monsters), alter the appearance of objects, communicate on a mental plane, possess people by manipulating and controlling the darkness inside their hearts (which was how he corrupted Oroku Saki), grow in size, teleport, shape-shift, and absorb dark energy.
The Shredder has shown a very high degree of superhuman strength, as he was able to catch a full power punch from Silver Sentry and toss him into orbit with ease. He has been described as the most skilled warrior in the land before he betrayed the Ninja Tribunal. He can also transform into a dragon, which has massively increased physical strength, incredible durability, flight-capable wings, as well as a powerful dark energy breath attack.
It has also been noted that the Demon Shredder forms a spiritual link with anyone who takes the name and mantle of "The Shredder" for themselves. This link is believed to be why all subsequent Shredders tend to pattern their armor (and, in the case of Ch'rell, their human disguise) after the original appearance of Oroku Saki. In the final battle against the Tengu, Karai was able to use this link against the Demon Shredder by draining his powers.
Due to Shredder's incredible powers, he sees everything as a game and does not fully utilize his power unless he feels threatened. Because of this, the full extent of the Demon Shredder's power is unclear - his arrogance caused him to be weakened and stripped of his power by the Turtles and their allies before he could unleash his full potential. Even so, the sheer numbers and powers brought against him (a massive alliance of heroes and villains, the mystical power of the Ninja Tribunal, Karai's ability to drain his energy through their shared link, and the spirit of Hamato Yoshi) is a testament to the threat he posed to the world.