The Teenage Mutant Ninja Turtles (TMNT) or in the UK earlier known as the Teenage Mutant Hero Turtles (TMHT) are a group of fictional characters. They are four mutant turtles, who were taught how to be ninjas by a mutant rat called Splinter. The TMNT were created in 1983 by Kevin Eastman and Peter Laird, making their comic book debut in 1984. In October 2009, Nickelodeon purchased the rights from Mirage Studios.
The turtles are named after famous artists from the Renaissance period. Their names are Leonardo, Raphael, Donatello, and Michelangelo. They live underground in a sewer under Manhattan, and try to keep themselves hidden from people mankind in general, fearing humanity would never understand. While helping their friends, they often end up in trouble fighting crime and villan. Their enemies may vary from inner town street gangs to extraterrestrials. There are a few humans who know about them, a woman named April O'Neil and a man named Casey Jones, and some other people, depending on version. Some versions also use Casey Jones' grandmother's farmhouse in Northampton in Massachussetts as a hangout for the turtles.
Splinter's origin differs between versions. In some versions (Mirage, 2003, movies), he was originally a pet rat of Hamato Yoshi, ending up mutated. In other versions (1987 carton, Archie and the 2012 cartoon), he was originally a man, Hamato Yoshi, who ended up accidentally touching the ooze, and turned into a humanoid rat.
In the 1987 cartoon, their main antagonists are a Japanese ninjutsu master, Shredder (Oroku Saki), an extraterrestrial called Krang, and two mutant punks, Bebop and Rocksteady, while in the 1984 Mirage comics, Shredder ends up killed by the turtles in the first issue. Krang's appearance is inspired by the Utroms, an extraterrestrial race in the Mirage. The Utroms, however, aren't villains.