Due to various movie and television deals, the various TMNT films and television series have split between various companies, with having retained copyright and trademark until October 19, 2009, at which point the rights for the entire TMNT franchise were sold by co-creator Peter Laird to .
Upon TMNT's first arrival in the United Kingdom and Ireland the name was changed to "Teenage Mutant Turtles" (or TMHT, for short), since local censorship policies deemed the word to have excessively violent connotations for a children's program (in Ireland, however, the first season aired as "Teenage Mutant Ninja Turtles" before the change to "Teenage Mutant Hero Turtles"). Consequently, everything related to the Turtles (comic books, video games, toys, etc.) had to be renamed before being released in these nations, as well as in the German-speaking countries.
The second animated series (2003–2009) was a co-production between Mirage Studios and 4Kids Entertainment. Nickelodeon's October 19, 2009 buyout of the TMNT franchise included an approximate $9.75 million payment to 4Kids to terminate its right to serve as the merchandise licensing agent prior to the scheduled expiration of the representation agreement in 2012. Due to the buyout, all future TMNT film and television series rights are owned by Nickelodeon. Nickelodeon also gained the rights to the 2003 series after terminating 4Kids' contract.
The Turtles engaged in a greater amount of overt violence in the pages of the early Mirage comic book series by Eastman and Laird. As the TMNT were introduced into the mainstream, they were radically redesigned. In issue #19 of , the creators published an editorial addressing any possible concerns of readers as a result of this. It stated, in part: "We've allowed the wacky side to happen, and enjoy it very much. All the while, though, we've kept the originals very much ours – forty pages of what we enjoy and want to see in our books, whether it comes from our own hands or from those of the talented people we work with." In the film , the original Mirage Turtles refer to their descendants as "sell-outs", in reference to their colorful accessories (the originals are conveyed in black and white).