DC Extended Universe HBO Series

The DC Extended Universe has several television series which air on HBO. They are set in the same universe as the films, and characters from the films often appear in the series. The series are all distributed by DC Films, with Geoff Johns acting as producer. The series include Guardian, Batgirl, Superboy, and the crossover Young Justice. Many have noted that the exploration of the universe in another medium is similar to that of Marvel's Netflix series, though Johns made sure to differentiate by including more characters from the films, which Marvel's series rarely did.

Guardian
The first series to air on HBO was Guardian. Guardian focused on the characters Mal Duncan and Jim Harper, two Metropolis police officers. The series is set between Batman v Superman: Dawn of Justice and Justice League, as the death of Superman is a major element of the story. Duncan and Harper work in the slums of Metropolis, often called "Suicide Slum", which has been taken over by gangs following Superman's death. After witnessing blatant corruption in the police and the gang violence on the streets, Duncan decides to take action outside the law. While Duncan is technically the main protagonist, the series gives nearly equal focus to both Duncan and Harper, including a subplot regarding Harper's past and the laboratory known as Cadmus.

Batgirl
Despite being the first series developed, Batgirl aired second after Guardian. Batgirl was initially planned as a film written and directed by Joss Whedon, who was brought in as showrunner. The series focuses on Barbara Gordon, the daughter of Commissioner Gordon, former protege of Batman, and former love interest of Dick Grayson. In the show, set some time before Justice League, Barbara once again assumes her vigilante title and goes on her own investigation while Batman is out of town. The primary villain of Batgirl is Victor Fries, a.k.a. Mr. Freeze. Whedon chose Mr. Freeze because he felt that he wasn't an outright evil villain, and people could sympathize with him.

Superboy
The third series to air was Superboy. Following the events of Justice League, Superman has returned to the world. Unbeknownst to him, he has a clone. Kon-El, a.k.a. Conner Kent, was created by Cadmus Labs in "Project Kr", an ARGUS-run project determined to clone Superman after his death. Conner has been living on his own in Metropolis for several months when he is approached by Amanda Waller, who offers for him to work for her at ARGUS. Without much of a choice, Conner agrees and begins to assist on ARGUS missions, though he is constantly skeptical of Waller's true intentions.

Young Justice
The fourth series, Young Justice, is currently in development and will be a crossover between the three series and the films. The series will feature several younger heroes teaming up against Talia al Ghul, daughter of Ra's al Ghul, who is leading her own rogue group of assassins from the League of Shadows, who is working with billionaire mastermind Lex Luthor.