Blackfire's Cult

Deacon Blackfire's Cult is a religious cult led by Deacon Blackfire, a power-crazed priest who, by his own word, claimed to be an over 100-year-old shaman who declared himself immortal and begun brainwashing people to join his cause.

The cult is made up of the downtrodden, homeless and less fortunate elements of Gotham City whom Blackfire gave food and shelter while brainwashing into devout religious extremists.

Arkham Knight Incident
The journalist Jack Ryder was investigating a mysterious cult leader named Blackfire, listening to his messages, examining the interrogations of his cultists, and reporting on the discovery of bodies. He continued with his investigation until he deduced Blackfire's whereabouts at the Lady of Gotham then went to investigate. When Ryder arrived there, he was captured by the cult and imprisoned, with Blackfire intending to use him as a human sacrifice.

Unbeknownst to Blackfire, however, Batman, suspecting that Ryder would get himself into trouble, followed Ryder's trail to the Lady of Gotham, arriving just as Blackfire and his followers were beginning the ritual. Blackfire, unfazed by Batman's arrival, ordered his cultists to attack and slay Batman as another "sacrifice".

Despite their superior numbers and fanaticism, the cultists were soundly defeated by Batman who then attacked Blackfire and knocked him unconscious, barely stopping him from murdering Ryder. Blackfire and the rest of his cult were all locked up at GCPD, where Blackfire would continue to preach.

Trivia

 * Unlike most other criminals found throughout Gotham City, who are little more than common criminals, thugs, and other amoral delinquents, Blackfire's cultists are strictly religious, and their objective is not power or personal gain but the blessing of God.