Krang

Krang (also spelled Kraang) is a fictional supervillain appearing in "Teenage Mutant Ninja Turtles"-related media, most frequently in the 1987 animated series and its associated merchandise, such as the "Teenage Mutant Ninja Turtles Adventures" comic book and most of the classic "TMNT" video games. 
Krang's first comics appearance was in "Teenage Mutant Ninja Turtles Adventures" vol. 1, #1, published by Archie Comics in August 1988. In the 1987 TV series, Krang was voiced by Pat Fraley. He is still one of the primary antagonists to the Ninja Turtles, appearing as General Krang in the 2012 IDW comic publication. The character made his first live action appearance in the 2016 sequel, "", with his voice provided by Brad Garrett.
Krang was created by David Wise, with inspirations from the Utroms, to supply the Shredder with extraterrestrial technology.
In the 2012 series, Krang is not Krang, but "the Kraang" and is a plural name for a species of aliens.
Abilities.
In the final season of the 1987 animated series, Krang showed signs of psychic powers when he hypnotized one of Lord Dregg's soldiers into obeying his and Shredder's commands, saying it would only work on weak willed people.
Relating to the Utroms.
Krang's physical appearance was inspired by the Utroms from the original TMNT comic book.
IDW Comics.
In the IDW Comics Krang is both an Utrom and a denizen of Dimension X. He is the heir of Quanin, the former Prime Minister of the Utroms' ruling council who appointed himself Emperor and aggressively expanded the Utrom domain into an empire. However, his megalomanic expansion drive both deprived his home planet of its most essential natural resource, the Ooze, and incited rebellion among the subjugated people of Dimension X, eventually leading to the destruction of Utrominon. Krang, who was as brutal as his father but opposed his uncautious politics, fled with a few survivors of his people through an interdimensional portal to Burnow Island on Earth, where he established a base from which he intended to terraform this world into a new home for his people.
In order to augment his troops, Krang, initially disguised as a despotic human warlord, forms a business relationship with Baxter Stockman, head of the genetics research institute "Stock Gen", and supplies him with Ooze, which could be used as a natural mutagen on Earth's organisms. It is through Stockman's experiments that the Teenage Mutant Ninja Turtles and Splinter evolve into intelligent, humanoid mutants. When the Turtles learn of Krang's genocidal plans thanks to their human friend April O'Neil, a former intern at "Stock Gen", they, together with their ally, the Fugitoid (a former Neutrino scientist whose mind is trapped in a robot body and who was forcibly conscripted by Krang to complete his terraforming machine, the Technodrome), and the Foot Clan stop Krang from destroying the Earth, and the Utrom warlord is surrendered to the Neutrinos for trial for his numerous war crimes.
While imprisoned on Neutrino, Kraang hires the bounty hunter Hakk-R to eliminate several material witnesses in order to get the trial cancelled, but Hakk-R fails thanks to the efforts of the Turtles. Eventually, Krang is found guilty and sentenced to permanent exile from Dimension X on Earth. However, Leatherhead, one of his former victims and a key witness in the trial, refuses to accept the mild verdict and kills Krang by devouring him. However, as the Fugitoid belatedly realizes, the Utroms possess a natural parasitic physiology, enabling Krang to regenerate himself and take possession of Leatherhead's body.
2003 series.
While he did not appear as a villain or major character in the 2003 series, there was an homage to Krang in the episode "Secret Origins Part 3". As the Utroms are all walking to the transmat to go back home one of them complains, "I hate walking on my tentacles". Then, another Utrom replies "Oh, shut up, Krang!". This Krang was voiced by Wayne Grayson.
Krang also appears in the 2009 crossover film, "Turtles Forever", in which he, Shredder and the Turtles from the 1987 show end up in the 2003 universe. Although Shredder was able to find his 2003 counterpart, he was unable to find Krang's, even though he exists in this universe (albeit as a regular, non-evil Utrom). Krang is voiced here by Bradford Cameron.
2012 series.
An alien species based on both Krang and the Utroms appear in the 2012 Nickelodeon show, named The Kraang. Kraang Prime is the leader of the hive mind and was a normal Utrom scientist until he made the mutagen, which he used to mutate himself into Kraang Prime. He then used his powers to enslave most of the Utroms into becoming hive mind slaves.