The Shredder is the name given usually to the main villain of the Teenage Mutant Ninja world. There have been many forms of Shredder's but they all share the same goal of world domination.
The Original Shredder Tengu was a large unknown demon, According to the Ancient One, no knows what level of the dark depths spawned him, but back in the year 300 AD in Hamoto, 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, lead 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.
Tengu ShredderThough 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.
Oroku Saki was eventually defeated by the four Dragons who had gained mystical powers, Saki was placed in a special coffin which would trap him forever. After his defeat, his loyal minions known as the Foot Mystics, 5 powerful beings which were one of the 5 natural elements: Water, Fire, Metal, Wind, and Earth. The had their true powers limited and were controlled by an amulet known as the heart of Tengu, which gave the owner full control of the Msytics.
Utrom ShredderCh'rell also known as Torrinon, Kako Naso, Duke Acureds, was an escaped Utrom alien criminal who crashed landed on Earth in Japan around 700 years after the defeat of the Oroku Saki the Tengu Shredder. Ch'rell stole a Utrom exo suit and placed Samurai armour it and took control of the Foot clan. Ch'rell took the name of the Shredder to gain fear and respect. Ch'rell later got possesion of the Heart of Tengu which her used to control the Foot Mystics.
Ch'rell was viewed by many such as the Ancient One and the Ninja Tribunal to be nothing but an alien bug who is not the true Shredder.
Ch'rell was the main Shredder until the Turtles defeated him and the Utroms exiled him to Mor Tal Gal a ice astroid.
Ch'rell eventually returned with help from the 1987 Ninja Turtles Shredder, his other dimension counterpart. However he was defeated and apparently killed.
KaraiAfter the exile of her adopted Father, Karai took control of the Foot clan. She soon became the new Shredder wearing her own armour based on Ch'rell armour.
As The Shredder, Karai was the primary villain throughout the show's fourth season. It was the fact that she had taken up the mantle of The Shredder that made her a target for the original Oroku Saki in The Lost Season, but also what allowed her to weaken him using a psychic bond.
Cyber ShredderA cybernetic engram of the Utrom Shredder Ch'rell. When the Turtles are sent by Viral into a not-so-distant future, they encountered three Shredders: the Demon Shredder, the Utrom Shredder, and a new Cyber Shredder, he attacked them a couple of times until the Turtles escaped to the present, where Viral followed them and escaped to the internet. While searching for a source to recharge herself, Viral draws the power from a data vault belonging to the Foot, accidentally transforming herself into the Cyber Shredder the Turtles encountered in the future.
Shredder warsWhen the Turtles and their Master Splinter were trying to get home they were attacked by a virus like being called Viral who sabotaged their time window sending them to different places in time. One place they were sent to was the not so distant future, where the Tengu Shredder, Ch'rell the Utrom Shredder and the Cyber Shredder were at war, with their own Foot Ninja's fighting each other aswell.
The Tengu Shredder seemed to have the advantage over the two other Shredders with his powerful black powers. Ch'rell's Utrom exo suit was badly damaged in the battle while the three Shredders are trying to kill each other so they can get the Turtles. The three Shredders finally decide to unite against the Turtles but the Turtles managed to escape through the portal to safety.
1987 ShredderThe 1987 Shredder was the Shredder of the classic Teenage Mutant Ninja Turtles in the classic series back in 1987. In the 2009 Turtles Forever movie, the classic Shredder appears, with Krang, Bebop and Rocksteady and of cource the 1987 Turtles.
Here Shredder tried to form an alliance with the 2003 Shredder Ch'rell. However his plans backfired, even though he rescued Ch'rell from exile the 2003 Shredder and Karai take over his Technodrome.