In the 2003 TV series the origin of Sliver is never properly explained. However, it is suggested that, like the mainstream Splinter, he must have had a much more heartfelt relationship with his sons before he was corrupted by evil. He acts in this incarnation more than an evil version of Splinter and as an archenemy of the Super Turtles who, despite his alienation, wants to reunite with his sons and sees the extermination of all other life as a way to do that.
In another universe, where the Ninja Turtles are superheroes instead of ninjas, their master, referred to as the Sliver, was initially their foster father but was eventually corrupted by evil. When Michelangelo was stranded in this parallel dimension by the fused Ultimate Ninja and Drako, Sliver was planning to wipe out humanity with the Penultimate Nullificator. However, because the device destroys all life on the planet, the Sliver modified it so that his tower and everything inside would be spared. He also planned on turning the Super Turtles to the side of evil once the Nullificator was set off, catching them in a Utromidium cage that proved impervious to their powers.
However, Michelangelo, who had accompanied the Super Turtles, came up with a plan to set them free. By having Blobboid pose as him, he tricked the Sliver into thinking that in Mikey's home universe, he and his brothers ruled the Earth and that they were loyal to their master. When the Sliver released 'Mikey', Blobboid revealed himself and snatched away his control cane, releasing the other Turtles from the cage. Unfortunately, the Sliver had the same powers the Super Turtles had and had mastered them to a degree which made him superior to his students.
With the Super Turtles quickly incapacitated, Mikey was left alone to face the Sliver. Using his ninja skills, he trapped the Sliver in his own cage, but the Nullificator was still set to go off. Luckily, Mikey figured that they could reverse its function to go off inside the tower. Shellectro managed to reprogram the device, and the Super Turtles escaped before the Nullificator destroyed the tower with the Sliver inside it, while Mikey was pulled away from this dimension by the efforts of his father Splinter to reunite his family. Sliver, still trapped in the cage, is killed instantly when the tower is vaporized.
His armor is very similar to the Shredder's.
In the 2003 drawing series, he has all the strengths of his former proteges: gravity manipulation, electrostatic discharge and electrokinesis, size and shape transformation, and blobboids slimy consistency. However, he has much better control over these abilities, allowing him to use them all at the same time.