The Sliver is a super villain Rat from an alternate reality. He is Splinter's evil alternate dimension counterpart and the grueling, destructive former sensei of the Super Turtles. His blind loyalty to his Master Shreddarius has put him at odds with his students and has become one of their major, reluctant foes.
Mirage
The brilliant but conniving Dr.Shreddarius's creates The Terrorkinetics. These robotic protectors were commissioned by the corrupt Chairman Lucks to defend the Earth from supposed Alien Invaders. In reality they were constructs of evil design.
Lucks, a World Unifying Leader had a definitive hold on this Universes' power and was untrustworthy. Shreddarius own private experiments included four Turtle Super Soldiers in case Lucks decided to double-cross his scientific friend and betray their dual beneficiary :
Griddex ,Blobboid ,Gravi-Turtle , Shellectro.
The Super Turtles !!
But the chemicals and experiments eventually became unstable. An explosion rendered Shreddarius severely disabled.
A somewhat familiar lab rat, licking the wounds and absorbing the chemicals on Shreddarius would mutate into the militant master,The Sliver.
Unlike the warm,caring ,nurturing, disciplined and kind wisdom and love shared by the Master Splinter we know, Master Sliver is cold and relentlessness in his teachings. A drill instructor from hell, his treacherous methods in training Shredderius's Super Turtles almost destroyed them numerous times in the insane effort for them to become the ' Ultimate Soldiers '.
Two rebel leaders, Case & O'Malley would convince the Super Turtles of the truth behind Luck's evil, twisted hold on power and Shreddarius's subservience to maintain it. Sadly, Master Sliver was so blindly obedient to mad Doctor, he would not waiver that loyalty.
Defeated briefly by his former students in time, independent from his Master Shreddarius. The Sliver would return more powerful than ever.
2003 series
Resurrecting a tower in the middle of Megatropolis, Sliver's ultimate weapon of mass destruction : The Penultimate Nullificator.
With hopes in destroying all life outside of the Tower, a trap is set into motion to capture the Super Turtles ( with the Universal Phase - shifting Michelangelo we know in tow ).
With the failed infiltration of the Tower, the Super Turtles fall into the clutches of their Evil Father.
Some slight of hand and quick place switching between Mikey and this Universe's version of him creates a "A Parent Trap". But the shape-shifting Blobboid can only hold off Sliver for so long, but at least long enough to set his brothers free.
Sliver however proves too powerful for his sons, once again. Sliver has mastered and can mimic all of his sons' powers. Thus leaving Mikey to face and capture him in Sliver's own Utromidium laden cage.
With the doomsday device set to go off, the brainy Shellectro manages to reverse the device, instead of destroying the world outside the tower.. it implodes.
The solo TMNT and the four Super Ts barely manage to escape in to time to resurrect a statue to honor their Turtle Titan friend from Null Space.
Did the implosion destroy the crazed Sensei ?
With increased powers & frantic ambition to reunite his family so that they may fight at his side...
rumors of the unhinged Rat's demise may hold not a "Sliver" of truth !
Video Games
In Teenage Mutant Ninja Turtles 3: Mutant Nightmare The Sliver makes a guest appearance as a boss in a later shooting, first-person perspective portion of the game. Similar to the effect of the episode "Reality Check", the Turtles are blasted into other dimensions by Ultimate Drako. However, in the game the Teens fight in each universe and face off against The Sliver together.