The Gotham City Police Department (typically abbreviated as GCPD) are the primary body of law enforcement in Gotham City. Unfortunately, prior to the arrival of both Batman and James Gordon, the GCPD was almost universally corrupt, with many high-and-low ranking members of the force being involved in offences ranging from bribery to drug smuggling and even murder.
Under the leadership of Commissioner Loeb, who himself was on the payroll of mob boss Carmine Falcone, the GCPD were little more than thugs with badges. When Batman first appeared, the force opposed him not because they viewed him as a dangerous vigilante (though they would use this as a justification), but rather because his actions threatened their criminal activities. In their desperation to kill Batman they also showed a complete willingness to endanger innocent civilians. This group consists of about 19 members.
Fortunately, following the ousting of Loeb as Police Commissioner and James Gordon's eventual appointment to the position, the GCPD underwent massive reform and became a much more efficient and honest police force, albeit one that heavily relies on Batman's assistance.
In the video game Batman Arkham Origins they are again antagonists, this time attempting to collect the reward Black Mask has offered for Batman's head. They are led by Branden in their efforts.
The GCPD is prominently featured in the TV series Gotham. As with other depictions in the DC Universe prior to Bruce Wayne becoming Batman, the department is rife with corruption and moral ambiguity among its officers, save for one young detective, future GCPD commissioner James Gordon.
In the first season the department is under the control of commissioner Gillian Loeb, who is in the pocket of Gotham's most powerful crime boss Carmine Falcone (just like Batman: Year One). Young detective James Gordon is shocked by the corruption in the department, especially when he are involved in a conspiracy with the mob to frame criminal Mario Pepper for the murder of Thomas and Martha Wayne. Gordon is tasked to kill snitch Oswald Cobblepot in order to "get with the program" and is instructed to by his partner Harvey Bullock, although Gordon fakes Cobblepot's death. During the course of the first season Gordon comes into conflict with several officers and gets under the skin of Bullock, who has put behind any attempts at being a
"good guy" due to the mass corruption and tries to convince Gordon to drop fighting those above for his own safety. Despite this Gordon lets his mortality get in the way and he still works to take down the corrupt officers and the mob, which leads to him spending a few weeks as a security guard at Arkham Asylum as punishment. As well as getting into conflict with commissioner Loeb, Gordon has a run in with Arnold Flass who deals in drugs and murdered a witness to his crimes, but Gordon managed to have him locked up. Bullock eventually joined Gordon in his crusade against crime and were backed up by other officers, such as Captain Sarah Essen.
In the second season the GCPD aren't in much of an antagonistic role, especially after Gordon manages to get Cobblepot to help him force Loeb into resigning as commissioner with many of the cops reforming or at least becoming less corrupt. Essen is promoted to commissioner, but is killed when the Maniax led by Jerome Valeska attack the precinct and massacre many officers. A new captain named Nathaniel Barnes is assigned to the precinct and begins to work on clamping down on the corruption in the department as well as crime in Gotham City, which starts with him firing corrupt officers in the department (and arresting one) and later starting a task force known as "Strike Force", which involves a bunch of new recruits. Gordon appears to get on with his colleagues better this season, although he ends up leaving after forensics analyst Edward Nygma becomes a serial killer and criminal and sets Gordon up for the murder of an officer, although Gordon manages to prove himself innocent and Nygma is arrested and locked up.
Just like season 2 the GCPD are not depicted as an antagonistic force in season 3, with bigger threats such as the Court of Owls essentially taking over as the major villains of the series. Unfortunately, Barnes ends up being infected with tainted blood which belonged to the now-deceased sister of madman Jervis Tetch, Alice Tetch, which leads to his inner demons and darker nature to come to the surface, resulting in him becoming a murderous vigilante to tackle the crime in the city, rather than work by the book like originally. Barnes is eventually detained and kept at Arkham Asylum, with Bullock becoming acting captain in his place.