Teenage Mutant Ninja Turtles (also known as Teenage Mutant Hero Turtles in some regions) is an American animated television series produced by Fred Wolf Films and based on the comic book characters created by Kevin Eastman and Peter Laird. Set in New York City, the series follows the adventures of the eponymous Teenage Mutant Ninja Turtles and their allies as they battle the Shredder, Krang, and numerous other villains and criminals. The property was changed considerably from the darker-toned comics, to make it more suitable for children and families.

The pilot was shown during the week of December 28, 1987, in syndication as a five-part miniseries, and the show began its full-time run on October 1, 1988, and ended on November 2, 1996. The show was the first television appearance of the Teenage Mutant Ninja Turtles, and helped launch the characters into mainstream popularity, becoming one of the most popular animated series in television history. Action figures, breakfast cereals, plush toys, and other merchandise featuring the characters appeared on the market during the late 1980s and early 1990s and became top sellers worldwide. By 1990, the series was being shown daily on more than 125 television stations.

Characters from the show have been included in crossovers with later entries of the franchise, including the 2009 film Turtles Forever and recurring roles in the 2012 TV series for Nickelodeon.

The origins story in the 1987 television series deviates significantly from the original Mirage Studios comics. In this version, Splinter was formerly human, an honorable ninja master named Hamato Yoshi who studied art history as a hobby. He was banished from the Foot Clan (a Japanese dynasty of ninjas founded by one of his distant ancestors) after one of his students, the power-hungry and seditious Oroku Saki (who resented Yoshi's leadership within the clan and aspired to usurp him), set him up for an offense against a visiting master sensei. Disgraced, Yoshi was forced to leave his native Japan and relocate to New York City, where he began living in the sewers with the rats as his only friends. Saki was given command of the Foot Clan, which he corrupted and transformed into a criminal organization.

Sometime later, Yoshi adopted four turtles after they were accidentally dropped into the sewers by a young boy named Chester Manley. He returned from his explorations around New York City one day to find the turtles covered with a strange glowing ooze. This substance caused the turtles, who were most recently exposed to Yoshi, to become humanoid, while Yoshi, who was most recently exposed to sewer rats, became a humanoid rat, and was given the name "Splinter" by the turtles. Yoshi raises the four turtles as his sons and trains them in the art of ninjitsu. He names them Leonardo, Donatello, Raphael and Michelangelo, after his favorite Italian Renaissance artists.

Oroku Saki eventually leaves Japan and tracks Yoshi to New York City, where he intends to destroy him once and for all. It is also around this time that he begins working with Krang, a disembodied alien brain from Dimension X who ruled his native realm with an iron fist until he was stripped of his body and banished to Earth. Saki takes on a new pseudonym, "The Shredder", donning a suit covered with razor spikes, and complemented by a long purple cape, a metal samurai helmet, and a metal mask over his mouth. Since leaving Japan, his ambitions have grown from usurping leadership of the Foot Clan to world domination. To this end, Krang provides the Shredder with a vast array of powerful technology from Dimension X, including the Technodrome, and funds most of his schemes throughout the series.

It becomes clear early on in the series that the mutagen which transformed the Turtles and Splinter into their new forms was dumped into the sewers by Shredder in an effort to murder Yoshi, as he had mistakenly believed it to be a deadly poison rather than a transformative agent. After several years of training under Splinter, the Turtles set out to find whoever is responsible for their transformation, and upon learning that Shredder was behind it, they vow to put an end to his ongoing criminal career and restore Splinter back to his human form. Along the way, they rescue and befriend Channel 6 news reporter April O'Neil, who becomes one of their strongest allies. The Turtles, who had rarely left the sewers prior to meeting April, also began to take on the role of semi-vigilante crime fighters. Despite this, they frequently have to deal with citizens misunderstanding them, largely due to the efforts of Channel 6 newsmen Burne Thompson and Vernon Fenwick, who both distrust the Turtles and frequently and wrongfully blame them for the trouble that Shredder and Krang cause. As a result, they mainly have to rely on April (either via Turtle-com, or Channel 6 news reports) to inform them of crimes in the city, and to counteract Burne and Vernon's smear and bad-tempered campaigns against them with her own news coverage of the Turtles, portraying them as a force for good. Reluctant to expose themselves to the outside world, the Turtles initially wear disguises whenever they leave the sewers, although this is slowly relaxed as the series progresses and they gain the trust of the broader populace, whom they have saved from Shredder and other villains on many occasions.

Shredder, Krang, Bebop & Rocksteady, Baxter Stockman, and their legions of Foot soldiers repeatedly try to destroy the Turtles and take over the world. Much of their quest for world domination hinges on repowering Krang's mobile fortress, the Technodrome, and bringing it to the Earth's surface, as it was either buried deep under New York City (Season 1), stuck in Dimension X (Seasons 2 and 4), embedded in the Earth's core (Season 3), stranded in the Arctic (Season 5), or at the bottom of the Arctic Ocean (Seasons 6 and 7). However, their plans always fail, often landing the villains in humorous predicaments. Some episodes feature other minor villains, such as the Rat King, Leatherhead, Slash, General Traag and Granitor, and many others, or involve the TMNT getting themselves and the city out of a mess that they had inadvertently caused.