Jeremy Davies, best known for his roles on Lost and Justified, will play Dr. John Deegan, a doctor at Arkham Asylum, in the upcoming Arrowverse crossover.
Dr. John Deegan is described as "a doctor at Arkham Asylum For the Criminally Insane in Gotham City, but he might just be crazier than the inmates he treats. His machinations will draw Green Arrow, The Flash and Supergirl to Gotham City."
There was a character named Jack Deegan who appeared in 1941's Batman #4. He was a villain recruited by The Joker and named the Jack of Diamonds. He died in his only appearance.
The Gotham-centric crossover will also introduce Ruby Rose in the role of Batwoman, setting the stage for that character to get her own show.
"We'll do a pilot for midseason, whether it goes to series, I cannot tell you," CW honcho Mark Pedowitz said at the TCA summer press tour. "We have five [DC shows] on the air and just added a sixth night."
Grimm star Elizabeth Tulloch has been cast as Lois Lane in the story, which begins on The Flash on Sunday, December 9 at 8 p.m. and runs through that week's episodes of Supergirl and Arrow.
Gotham will appear for the first time on The CW in this episode, although it has been referenced several times on Supergirl and has periodically shown up as a potential destination for the Waverider on DC's Legends of Tomorrow.
"To see Flash and Superman together and to be one of the guys in the suits is something I'm definitely pretty excited about," The Flash star Grant Gustin said. "It did feel like something they would always save for the features to be honest. But I feel like the Arrowverse has kind of been changing that stigma with the whole TV is the lesser medium. I think it kind of doesn't matter these days with the streaming and content's kind of everywhere. So, it is cool to see us kind of rise to even another level and bring all of us together for these crossovers. It's pretty epic."
The currently untitled Arrowverse crossover will take place across three nights, kicking off on Sunday, Dec. 9th on The Flash at 8 p.m. ET. It continues on Arrow Monday, Dec. 10th at 8 p.m. and then finishes up on Supergirl Tuesday, Dec. 11th at 8 p.m. ET.