https://youtube.com/shorts/NTiUS36nLNM?si=1E7QvZ3K9wRV8rbH
Years ago, Michael Lane was part of a program to create the ultimate crime fighter. Instead, it turned him into an insane criminal. Thwarted by Batman, Michael confessed his sins to a priest of the religious sect, The Order of St. Dumas. They recruited Michael to fight evil as their azrael, who wore the mystical Suit of Sorrows and wielded the Sword of Sin.
:The Order of St. Dumas:The Order of St. Dumas is a secret society which has become based in Gotham City. To date, the only member whom has been seen is azrael.
:Before arkham City Incident: The Order of St. Dumas claimed to have been around for over 500 years; during their existence they fought corruption in Gotham through unethical means.

Michael Lane would eventually be found by the Order. Seeing it as an opportunity to redeem himself for his past, Michael Lane willingly took up the title of azrael and devoted himself to the Order and their goals, not Realizing that they were secretly stripping him of his free will in order to make him into the perfect weapon.
:Arkham City Incident: The Order of St. Dumas had long wanted to be the guiding force against crime and corruption in Gotham. When news came that Bruce Wayne/Batman was Rumored to be currently in arkham City, the Order jumped at the opportunity. Sending azrael out to earn Batman's trust. The Order provided the Dark Knight with a cryptic message that would come true one year later.
Arkham Knight Incident
On the night of Scarecrow's revenge, amongst all the chaos, the Order finally decided to make their move. Sending Azrael to trick and kill Batman, so that they could take his place. But Batman, whom had grown suspicious of Azrael and the Orders motives, discovered the truth, and, depending on the choice, either beat Azrael unconsious and left for the police or freed Azrael from his mind control.

If the latter option is chosen, then Azrael, freed of his mind control, will vow revenge against the Order for what they have done to him.

Behavior
To date, not much has been revealed about this shadowy organizations methods. However, it can be safely assumed that they share similar views as the League of Assassins. They appear to believe that Gotham's savior has to be willing and relentless to the point where they will do anything, including kill, to get the desired result. Since Batman was clearly unwilling to go that far in his crusade, the Order decided that another would have to take his place.

Trivia
The leader of the group is voiced by Keith Szarabajka.
It remains unknown if the Order and the League know of each other.
Some fan theories include that the Order may a faction that broken off from the League, and some hoped that there would either be a confrontation or alliance between the two. This doesn't quite work out though, as the Order of Saint Dumas more similarly function as the Knights Templar.
The Order shares many similarities with the Knights Templar, a medieval Catholic Military Order who were one of the major participants of the Crusades for the Holy Land. They were lead by a man with the title of Grandmaster.
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