The Blue Templar was started as a way to police the police after Serpico and the Knapp Commission. Their original goal many of the original members left, and those left blue. Under them, the Blue Templar became 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 amongst themselves.
The Blue Templar was also willing to murder its fellow officers who tried to expose them, as they did with Det. 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.
The organization takes the role of being season one's main antagonist.
Det. Sonny Malevsky (deceased)