New York Police Department

The New York City Police Department, or NYPD, is the main law enforcement agency for New York City as they appear in many of the various media of Teenage Mutant Ninja Turtles, sometimes allied with the Turtles, or having no idea of their actions in helping to stop many of the villains that the Turtles fight on a routine basis.

1987 television series
In the 1987 episode, The Great Boldini, following the theft of a valuable gemstone from the local museum, the NYPD, under the command of Lieutenant Bronski and his second-in-command, Sergeant O'Flaherty, secure the museum and attempt to check anyone coming out, including Channel 6 reporter April O' Neil, and the trench coat wearing gentlemen with her, only to discover them to be the Turtles. Lt. Bronski immediately thinks they stole the gemstone, and has his officers draw their service revolvers in an attempt to apprehend them. Before they can, O'Flaherty, thinking them to be leprechauns, causes enough of a distraction to allow the Turtles to escape arrest, using April's news van to escape as O'Flaherty gives pursuit in a patrol car. The Turtles lose him as they escape through their sewer entrance to safety. Back at the museum, Lt. Bronski is shocked when an army of rats emerges out the museum's front entrance before the museum enters lock-down mode due to the sabotage of the museum security systems by the Rat King, preventing Bronski or his men from gaining entrance, and believing that the Turtles are behind it. When the Turtles return to rescue their friends, Zack and Caitlin, O'Flaherty catches them and places them under arrest again while also worried about arresting April as well if she's involved. However, the Turtles and April are able to convince the sergeant to allow them one hour to retrieve the gemstone and prove their innocence, or the Turtles will surrender willingly to the NYPD. Though hesitant to let them go again, O'Flaherty agrees to the one hour time limit, receiving a kiss of thanks on the cheek from April. Later, he arrives ahead of the other officers once the lock-down is lifted to see what is going on, and April reveals that the Turtles have caught the real culprits in the form of Don Turtelli and his cousin, The Great Boudini. O'Flaherty is given the stolen gemstone back by Zack, while the Turtles make their escape with Zack and Caitlin, leaving April to handle the rest. When Bronski and the other officers arrive, O'Flaherty takes full credit for the capture of the real criminals, but offers his thanks to the Turtles as well, calling them the "Teenage Mutant Ninja Leprechauns."

Live-action movies
The NYPD appears in the live-action movies as during the first movie, they are struggling to deal with a recent crime wave being performed by the Foot Clan with young teenagers, with Chief Sterns being the officer in charge of the investigation. April's boss, Charles Pennington's son, Danny, is also suspected of being part of the crime wave, having been arrested previously in one attempt at stealing, allowing Sterns to blackmail Charles with putting Danny in juvenile hall or Riker's Island unless he keeps April from getting too nosy in her news reports about the crime wave. Despite warning her about Sterns, April still takes a stab at him during her report, forcing Charles to fire her as a result. They also are presumably called to run security when the FDNY is called to extinguish the fire that was now engulfing April's apartment and antique store following a scuffle between the Turtles and the Foot that originally sparked the inferno. Following the Turtles emerging triumphant over the Shredder and his presumed death in the back of a garbage truck, Sterns arrives with several cruisers, arresting those Foot Clan ninja who failed to flee in time when the police arrived, and then confronting the teenagers who had been part of the crime wave, demanding to know what is going on. Hoping to avoid severe punishment from the judge, and to make amends for their actions, the teens confess to the location of the Foot Clan's hideout in the East Warehouse, and Sterns orders men over there to investigate, leading to where many of the Foot Clan are apprehended by the NYPD, and they are better prepared for the Foot in the future.

In the sequel movie, the NYPD is called by Keno after the Turtles incapacitate a large group of robbers attempting to rob an underground mall before Keno caught them, and the Turtles arrived to deal with them personally. Meanwhile, with many of the Foot behind bars, the survivors are forced to retreat to their fall-back spot in the junkyard to avoid being caught by the NYPD as well. Following after the Shredder unleashes his mutants, Tokka and Rahzar, on an unsuspecting street, leaving a path of carnage and destruction in their wake, Sterns is on scene in the morning with the NYPD, FDNY, DSNY, and other New York City public services to clean up the mess and deal with the wounded, reporting on the condition of the area to April and other news channels before requesting to end the interview so he can resume the investigation. Once away from the camera, April confronts him about if he noticed anything out of the ordinary, referring to any clues that the Foot Clan are back and at it again, but Sterns makes it clear he knows what she is talking about, but does not want to go public about it and possibly cause a panic. April agrees, and leaves Sterns to return to his precinct, knowing full well this is not a job for New York's Finest, but for the Turtles. The NYPD is called later when the Turtles are fighting Tokka and Rahzar in the nightclub where Vanilla Ice is performing, but when the manager sees that the crowd enjoys what's happening, he changes his mind and tells his assistant to tell the dispatcher that the NYPD are not needed.

2012 television series
The NYPD makes numerous appearances in the 2012 series as they investigate the aftermath of many of the Turtles' dealings with the Kraang and the Foot Clan around Manhattan. At one point, two Kraang are able to use their Kraangdroid bodies to disguise themselves as NYPD officers to arrest Casey Jones, but Casey is able to overpower and defeat them. However, in the chaos of the invasion by the Kraang with the Technodrome, and later by the Triceraton Armada, the NYPD find themselves outnumbered and outmatched and can do little to prevent Manhattan becoming occupied by the Kraang until the Turtles are able to send them back to Dimension X, allowing them to begin rebuilding the city, and then stopping the Triceratons from occupying the city until their doomsday weapon activates, sucking New York, along with the rest of the Earth, to its doom. With the Earth's restoration by the Fugitoid turning back time 6 months to before the Triceraton invasion, the NYPD are able to continue protecting New York City until the Turtles return to defend it once the Triceraton doomsday weapon is destroyed for good before it can be used on the Earth.