In the 4th Century, an evil Tengu known as the Shredder began to wreck havoc across Japan, and planned to dominate 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 him on the astral plane, and offered him power and the world in exchange for his soul. Immediately, Saki's dark side allowed the Shredder's soul into his own before Saki destroyed the Shredder's empty husk.
The five warriors returned to the Emperor, who declared 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, conquered Japan, and inverted the symbol to his own. The other Dragons went around the world, and learned ancient arts from mystic masters, until they returned, and transcended mortal boundaries. The four Dragons battled against their former comrade in a magical battle, and manifested their worldly avatars. Ultimately, the Shredder was defeated, but could not be destroyed, so the four Dragons sealed him in a coffin and hid his Helmet and Gauntlet. The four Dragons kept watch over those objects, for if they were to be reunited then the Shredder would rise again. To help them prevent the Shredder's revival, the four Dragons declared themselves the Ninja Tribunal and taught their secret arts 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, and played on the legend to gain respect.
The Foot Mystics sent a Bone Demon, that was 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, managed to hit the amulet, and allowed him to be defeated by the Ancient One and Master Splinter. The Ninja 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 Ninja Tribunal and took the artifacts to New York, where they revived the Shredder so that he could take revenge on Karai, who usurped his title. Shredder prowled his way through the Oroku Saki Memorial Library to get to Karai, but she proved resilient with the magic-based weaponry that 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, and caused Karai to believe that she had struck her master. The Shredder's face then changed to his undead form, and he said that mortals were such fun to toy with, which clarified that he messed with her. Shredder then turned Karai's 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 Shredder to reveal his demon and Undead Minions that he summoned while in the Netherworld, and turned the top of the tower into a graveyard. Shredder's 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, and wounded Karai. The Turtles summoned their dragon avatars to battle the Shredder, which sent him and the Five Mystics plunging down to the ground. As the Turtles retreated, the Shredder looked at the modern world and announced his plans to modify it for his own.
After he captured the Mayor's Office, the Shredder began to turn it into his citadel with an expanding dome, and began to transform New York into a world of chaos, darkness, and monsters. But as Shredder required more energy to complete the transformation, the Five Mystics made sure that the city officials had created the Keystones in a triangle to amplify the spell. When the Turtles tried to reverse it by using the Keystones' power against Shredder, Shredder found out and was angry that the Five Mystics didn't inform him. He prevented the spell from being broken, and strengthened it to finish the transformation.
The Turtles, allied with their fellow Acolytes, the Purple Dragons, the Earth Protection Force, the Justice Force, and the Foot Clan, and 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 that they could separate his helmet and gauntlet. But as Shredder was rendered unconscious, Hun kicked him to make sure that he was dead, but Shredder woke up and threw him. Shredder then transported Splinter, the Ancient One, and the Turtles outside, where he rode on a demon horse, was armed with a trident and prepared for the hunt. He struck down the latter and went to attack Splinter when Hamato Yoshi manifested from the Turtles' Medallions. Yoshi snatched the Shredder's Trident and slashed him with it, which caused precious energy to leak from his armor. To repair himself, the Shredder restored New York to normal before he transformed into his dragon avatar. The Turtles also became dragons and battled against him, but the Shredder proved too strong. Karai began to sap Shredder's energy again, so he went to destroy her. But the Turtles struck back as Shredder slowly got weak, and reverted to his human form. Out of desperation, Saki tried to charge against his foes, but the Turtles tossed him around, and separated his gauntlet, which was crushed in Michelangelo's mouth, and helmet, which was stomped by Leonardo. When the Turtles returned to their normal forms, their acolyte amulets were destroyed, and they manifested Yoshi's spirit once again. Yoshi sliced the Shredder in half with his sword. In addition to the Shredder's physical form 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 could 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 engaging in battle with each other, while members of the Foot Clan who were 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 could be assumed that the Shredder had wished to fight at maximum power instead of diverting some power to summon his undead minions. It was worthy to note that this future did not occur because the principles of time travel suggested that this was an alternate future. Raphael commented on how that was a twisted future with three Shredders. It was a possible future, but it did not occur.
The Original Shredder Tengu
The Tengu Shedder was 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 knew 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. Saki dealt the final blow, and seemingly put an end to the demon for good and the five warriors became known as the Five Dragons.
Although it appeared that Saki had defeated the demon, in reality, he had struck a deal with the Tengu who promised him that he would make him a god among men by allowing the Tengu's evil spirit to merge with his human soul, and become the host to the greatest evil the world had ever known. Saki's betrayal plunged Japan into an age of darkness, and 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, did the Ninja Tribunal defeated and imprisoned their former comrade.
The Original Shredder was a being of pure evil: His goal was nothing short of total conquest, and he destroyed everything in his path on his way to achieve that aim. The Demon Shredder had a sadistic sense of humor, saw everything as a game, and toyed with his foes by using a mere fraction of his incredible power - however, he became much more serious if he came upon adversaries who threatened his power.
It should also be noted that even though Oroku Saki had allowed the Shredder Tengu to consume him, his personality remained dominant in their new form, although he was clearly influenced by the demon's soul. It is currently unknown what Oroku Saki's personality was like prior to his encounter with the Shredder Tengu.
The Demon Shredder was one of the most powerful beings in the TMNT Universe, with the ability to remake the entire Earth in his own image. Shredder mostly relied on his dark magic in battle, which became even stronger as more of the world's mystical practitioner. He could fire very powerful dark energy blasts, move objects, control and manipulate the elements, regenerate from injury, summon armies of Tengu (including demons, undead, and assorted monsters), transfigure 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, shapeshift, and absorb dark energy.
The Shredder was shown to have a very high degree of superhuman strength, as he was able to catch a full power punch from Silver Sentry and tossed him into orbit with ease. Shredder was described as the most skilled warrior in the land before he betrayed the Ninja Tribunal. He could also transform into a dragon, which had massively increased physical strength, incredible durability, flight-capable wings, as well as a powerful dark energy breath attack.
It was noted that the Demon Shredder formed a spiritual link with anyone who took the name and mantle of "The Shredder" for themselves. That link was believed to be why all subsequent Shredders tended 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 him, Karai was able to use that link against the Demon Shredder and drained his powers.
Due to Shredder's incredible powers, he saw everything as a game and did not fully utilize his power unless he felt threatened. Because of that, the full extent of the Demon Shredder's power was 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 Shredder (a massive alliance of heroes and villains, the Ninja Tribunal, the turtles summoning their dragon spirits, Karai's ability to drain his energy through their shared link, and the spirit of Hamato Yoshi) was a testament to the threat that he posed to the world.