Krang is an extremely intelligent warlord from Dimension X. He somehow took command of an army of Rock Soldiers under the leadership of General Traag, and stole the Technodrome, a powerful battle fortress, from its creator Drakus. Something then happened, that caused Krang to be stripped of his body and confined to a brain-like form, and to be exiled from Dimension X to Earth, along with his army and the Technodrome.

While on Earth, Krang allied himself with the Shredder, who, along with his robotic Foot Soldier army, moved into the Technodrome. In exchange, the Shredder had to design and build a new body for Krang, a human-shaped exo-suit. Shredder lived up to his part of the bargain in the season 1 episode The Shredder is Splintered, in no small part because he was unable to deal with the Turtles and needed Krang's help. Indeed, in the season 3 episode Shredderville, the Turtles visit/dream a parallel world in which they never lived, and Shredder had no problem taking over the world. In this world, Shredder abandoned Krang after his conquest was complete, leaving him with no body and a heavily-damaged Technodrome.

Krang's ultimate goal is to take over the Earth; it probably only became his objective after he was exiled on the Earth, but this point is never made clear. Every plan Krang conceives is either aimed at that goal, or towards the short-term objective of powering-up the Technodrome. He does not share Shredder's obsession with the Turtles; while Shredder sees them as mortal enemies, Krang seems to regard them more like annoyances to be destroyed when they interfere in his plans.

Counting from the first meeting between the Turtles and Shredder and Krang, Krang spent eight years in his Technodrome, either somewhere on Earth or in Dimension X, scheming to power up his battle fortress and take over the Earth. In the season 8 episode Turtle Trek, the Turtles destroy the engines of the Technodrome, trapping it and its inhabitants in Dimension X for good and putting an end to Krang's plans.

Krang spent the next two years in Dimension X, until he was contacted by Dregg (The Power of Three). Dregg arranged for him and Shredder to come back to Earth, to help him fight the Turtles. However, Dregg betrays them, and drains Krang's intelligence. Shredder escapes and restores Krang (A Turtle in Time), but Dregg captures them again. Finally, the Turtles spoil his plan and transport Shredder and Krang back to Dimension X (Turtles to the Second Power).

In the series finale Divide and Conquer, the Turtles return to the Technodrome to take Krang's exosuit, which they need to fight Dregg. Krang is nowhere to be seen. But it is assumed that he is still somewhere in Dimension X.

In the Archie Comics series, Krang was depicted as far more evil and wicked than in the cartoon. He was said to have the blood of whole races on his hands.