The Blue Templar was an organization within the NYPD, created as a way to police the police, after Serpico and the Knapp Commissions were formed to investigate corruption within the NYPD in the 1970s. However, the organization's original goal was lost after many of the original members left, and those who remained became corrupt themselves. The Blue Templar would eventually become involved in various criminal enterprises, including but not limited to black op drug busts wherein they would kill any witnesses and steal their drug money to be later distributed among themselves.
The Blue Templar was also willing to murder fellow police officers who tried to expose them, as they did with Joe Reagan and attempted to do to his younger brother Jamie. After the attempt on Jamie's life, the Reagan family, along with a few close friends in the NYPD, banded together to bring down the Blue Templar, which culminated in the organization's mass arrest and Det. Sonny Malevsky's confession to murdering Joe before turning his gun on himself. After these events the Blue Templar presumably became defunct, and all the officers involved with the organisation presumably jailed. The organization takes the role of being season one's main antagonist.