Warning: The following contains SPOILERS for Batwoman, season 1, episode 19, "A Secret Kept from All the Rest."
"A Secret Kept From All The Rest," the penultimate episode of Batwoman's first season, contained an Easter egg that revealed Azrael exists in the Arrowverse. First appearing in Batman: Sword of Azrael #1 in October 1992, Azrael was a hereditary title handed down from father to son among one line of a secretive knighthood known as the Order of Purity, who had splintered off from the Order of St. Dumas, much as the Order had splintered off from the Knights Templar during the Third Crusade.
Named for the Angel of Death, Azrael was meant to act as the Order's enforcer and chief assassin. The most recent Azrael, Jean-Paul Valley, rejected the violent path preached by St. Dumas and became an ally of Batman, even briefly taking up the mantle of the Bat when Bruce Wayne was seemingly paralyzed for life following the Knightfall storyline.
The Gotham City of the Arrowverse was seemingly left without protectors following Batman's abandoning the city. Mention has been made of both Robin and Oracle existing in the Arrowverse, but nothing had been said about what happened to them or where they are now. There had never been any indication that Azrael might have ever been one of Gotham City's protectors until mention was made of Azrael, the Order of St. Dumas and the Order of Purity in the encrypted journal of Bruce Wayne's ally, Lucius Fox.
Batwoman's "A Secret Kept From All The Rest" saw Luke Fox abducted by Alice and Hush to decode his father's journal, which reportedly held the secret for penetrating the near-indestructible BatSuit. While Luke was able to crack the code his father had used to make his journal unreadable, it turned out Lucius had another trick; a special pair of smart glasses which automatically translated the journal for whoever looked at it while wearing the glasses. Though only a page of the journal was briefly visible, it told a story, taken directly from the pages of Detective Comics, which spoke of the origins of Azrael's armor.
The entry described the history of the Suit of Sorrows; a mystic suit of armor forged by the Order of Purity, which Batman was given as a gift by Talia al Ghul. Legend had it that the Suit of Sorrows would grant its wearer enhanced speed and strength, but only if they were pure of heart. Anyone else who tried to wear the armor would be driven mad. The journal entry ended with a note that Batman learned the history of the Suit of Sorrows from a member of the Order of The Pure and that he kept it as a trophy in the Bat Cave before it was taken up by the new Azrael.
This history lines up almost precisely with the history of the Suit of Sorrows in the comics, where it was stolen from the Bat Cave and given to a man named Michael Lane, who became the new Azrael. This raises several questions about the current status of the Order of St. Dumas and the Order of Purity/Order of The Pure and who wears the Suit of Sorrows now. It seems likely, given how the writers of Batwoman love to hint at things to come in their Easter eggs, that we may see Azrael return to Gotham City in Batwoman season 2.