The Court of Owls is a secret organization centuries old with immense power and influence embedded into the very architecture and history of Gotham City. The court would select a trained and strong athletes taught by the Haly's Circus, and the few chosen ones would become their Talons (assassins). In fact, Dick Grayson was supposed to one of their Talons, as we find out later in the Night of Owls story arc, but, fortunately, Bruce adopted him, before the disaster could happen. The myth of their existence has been past down for generations in an old Gotham nursery rhyme, which reads:
Beware the court of owls, that watches all the time, ruling Gotham from a shadow perch, behind granite and lime. They watch you at your hearth, they watch you in your bed, speak not a whispered word of them or they'll send the talon for your head.
Though they first made their appearance in the second volume of Batman, creator Scott Snyder had planted hints and easter eggs of their existence in his Detective Comics run "The Black Mirror" and the mini series Batman: Gates of Gotham.
Major Story Arcs
Sometime after Bruce Wayne's creation of Batman Incorporated, he feels it is time to return to his home city of Gotham. Bruce feels confident in his return to Gotham, and decides to use his wealth and influence to revitalize the city, announcing his plans to most of Gotham's elite. His announcement party is interrupted when he overhears Commissioner Gordon receiving a police report of a mysterious murder. Bruce arrives to the scene as Batman, meeting with Harvey Bullock, where they find body, a true "John Doe" with no identity, crucified with multiple antique throwing knives, all of them marked with the image of an owl. Bullock wonders if the symbol on the knives has anything to do with an old nursery rhyme, but Bruce is preoccupied searching for clues, eventually finding skin under the victim's fingernails. While he sends the skin cells to Alfred for DNA recognition, Bruce finds a secret message proclaiming "Bruce Wayne will die tomorrow." Shortly after, Alfred finds the DNA test results to be startling, as the DNA of the potential killer is a perfect match with one of Bruce's closest allies, Dick Grayson.
When Bruce Wayne is attacked by Talon, he mentioned, "How I love killing Waynes," to which he was referring to Alan Wayne, Bruce's great, great-grandfather, in his later years that developed a severe paranoia about birds and felt they were conspiring against him. During the process of investigating his death, Bruce exhumes the body of Alan Wayne and discovers marble residue on the body, which leads Bruce, as Batman, to investigate where Alan Waynes body was found. Here, Batman was attacked by the Talon and is knocked out. He wakes an unspecified period of time later in the Court of Owls Maze, made of marble. Without his utility belt, Batman survives in the maze for 8 days, without food, his only sustenance being (possible drugged) water from a fountain, before escaping by blowing a hole in the floor and falling into a large underground river. The leader of the court of owls, what appears to be an old woman wearing a mask, then orders the current talon to be disposed of, and to wake all the other talons.
Bruce manages to escape the maze and later on in the story, it is announced that the Talons of the court will kill many important figures in Gotham and it is the Bat-Family's job to stop them. Batman fights Lincoln March, who claims to be Bruce's brother, even though he doesn't believe it. It is later revealed that Bruce actually had a brother, but he died when he was very young and Batman wouldn't remember him.
Soon after Haly's Circus comes to Gotham, Dick Grayson is attacked by an assassin who calls himself Saiko, proclaiming Dick is the "fiercest killer in Gotham" even if he doesn't know it. Dick survives the attack, but Saiko follows him to Atlantic City, where he gains the information from C.C. Haly that Dick Grayson and Nightwing are one in the same, after fatally injuring him. With Mr. Haly's dying breath, he tells Dick that he's giving him the circus, but there's a terrible secret that lays "in the heart" of the circus. It takes Dick some time to figure out what Haly meant, but he eventually decides to investigate the center ring of the circus, and inside he finds an old book with names, including his in it. (It also contains the name William Cobb, which was later revealed through solicitations to be the name of the Talon trying to kill Bruce.) When the circus heads back to Gotham, Saiko springs a trap for Dick at a Flying Graysons memorial show. It is here where Saiko reveals that he is Dick's old circus friend, Raymond, previously thought to have died in a car accident. He holds a grudge against Dick for if he had never left the circus, Raymond wouldn't have been taken by "them" and tortured into becoming a killer. Though not explicitly stating who "them" is, Raymond reveals that after Dick left, Mr. Haly had arranged for the Court of Owls to take Raymond, who they would torture until he broke, so they could train him to be a killer. But in the end, they felt as if Raymond wasn't good enough, so they left him alone in a forest to die, where birds would peck out his eyes.
Talon is a comic detailing the life of Calvin Rose, a former escape artist for Haley's Circus, and an escaped assassin for the Court of Owls. When he given the task of killing an innocent woman and her daughter, Rose decided to flee, and has been on the run ever since.
After hearing of Batman's encounter with them, Rose decided to return to Gotham City in order to see if the Court of Owls was defeated. When he is injured by one of the Talons, Calvin is rescued by a man named Sebastian Clark, who is also an enemy of the Court. Together, they decide to go after the Court of Owls, and stop them once and for all.
In their first mission together, Calvin goes the Orchard Hotel, where the Court's treasures are kept. His aim is to find the files on the two women he protects, but Sebastian wants to destroy the organization's financial status, as by doing so, the Court would be weakened. Rose expected to find the files in a safe, but instead he discovers a mask, belonging to the Orchard family. At that moment, Benjamin Orchard attacks Calvin claiming that the mask belongs to him. The Ex-Talon, finding himself at a weak spot against one of the Court's greatest warriors, blows up the treasure area, only before fleeing the location. Meanwhile, the Court of Owls notices the trouble Calvin is causing them, therefore they wake up Felix Harmon, the 'Gotham Butcher', in order to kill the only man ever to flee their clutches.
Batman Arkham Origins
The Court of Owls didn't make an appearance, nor a cameo appeareance in Rocksteady's Batman Arkham Origin, but the Court of Owls was referenced in the game. During Batman's first fight with Bane, there were statues of two owls that held throwing knifes, which heavily refers to the Court of Owls.
Alongside of that, the Court also got referenced with a book.