|“||Kraang's speculation of finding the turtles sooner than later was correct. Kraang rules.||„|
|~ A Kraang soldier after finding the Turtles at the docks|
They were involved in the creation of the mutagen that turned the title protagonists into mutant turtles. They launched invasions on New York in the finales to Season 1 and Season 2, managing to take over the city in Season 2. The turtles and the Mighty Mutanimals managed to banish the Kraang to their home dimension half way into season 3 and any know remaining Kraang, including Prime and Sub-Prime, were killed off by the Triceratons. They reappear in season 4 in "War for Dimension X" and "Trans-Dimensional Turtles", however, nothing about their position and fate changed because both of these episodes took place after the turtles time traveled, and the episodes themselves mostly took place in Dimension X.
All of the Kraang are voiced by Nolan North, who, ironically, voiced Raphael in TMNT (2007).
It was stated by the Queen Utrom in "War for Dimension X" that the Kraang were once peaceful Utroms themselves, however, they were mind controlled and enslaved by the power hungry scientist Kraang (who soon started calling himself Kraang Prime) and turned into mindless and emotionless virtual copies of himself. The Kraang would later engage the Triceratons in a massive war for control over Dimension X, they would later win the war when they used Zayton Honeycutt's energy source, renaming it "The Black Hole Generator", to obliterate the Triceraton's home planet. The Kraang would spent the next several thousand years trying to mutate worlds and universes to look like theirs, although they never succeeded because their mutagen was not perfected and only mutated people into the last thing they touched (normally animals or plants). The Kraang were also responsible for mutating primates into humans, injecting April's mother with Kraang DNA while she was pregnant, giving April her psychic powers, and accidentally mutating Hamato Yoshi and his pet turtles into Splinter, Leonardo, Donatello, Raphael and Michelangelo.
In the Series
In the series, The Kraang are multi-tentacled brain-creatures who came to Earth a millennia ago from another dimension to colonize it. Unfortunately for them, the Earth’s biosphere is not particularly hospitable to them, so they’re plotting to transform the Earth’s environment into something more suitable for their own kind – and destroy all human life! They brought the Mutagen Ooze with them from their own dimension, but it doesn't work as they thought it would, as the physical laws of our world are different from their own. They have been kidnapping scientists to help them modify it ever since. It has been revealed that it was the Kraang who were responsible for Splinter and the Turtles' mutation. The Kraang breathe a noxious gas that is toxic to humans and other Earthly life. Their ultimate goal is to mutate the entire planet using the mutagen and the Kraang-like powers of the Turtle's closest friend and Donatello's love interest, April O'Neil, whose mother and great-grandfather they experimented on before she was born. That way the Earth would become habitable for them and nothing else.