American television network The CW has cast gender-fluid actress Ruby Rose as the DC superhero Batwoman, entertainment website Variety reported on Wednesday (Aug 8).

The character, DC Comics' first openly lesbian superhero, will debut on an upcoming crossover episode expected to be aired later in 2018.

The annual crossover special set in Gotham City will bring together characters from The CW shows Arrow, The Flash and Supergirl.

It was also previously announced that The CW is developing a standalone series for Batwoman, which will air in 2019 if it is picked up by the network.

Rose, 32, is best known for her role as Stella Carlin in the Netflix prison drama series Orange Is The New Black.

The Australian has also appeared as an assassin and bodyguard in the John Wick series of action movies, and plays Jaxx Herd in the science-fiction horror movie The Meg released on Thursday.

She has dated women and is open about her gender fluidity. In a 2015 interview with Elle magazine, she said: "I definitely don't identify as any gender. I'm not a guy; I don't really feel like a woman, but obviously I was born one. So, I'm somewhere in the middle."

Batwoman, also known as Kathy Kane, was first introduced to the DC Comics universe as a love interest for its flagship hero Batman in 1956.

This was seen by some as an attempt to refute allegations of Batman's homosexuality in American psychiatrist Fredric Wertham's controversial book, Seduction of the Innocent, two years earlier.

Batwoman was later reimagined as a Jewish lesbian, now known as Kate Kane, in 2006.

Rose wrote in a post on Instagram that she was "beyond thrilled" to be cast as Batwoman.

"This is something I would have died to have seen on TV when I was a young member of the LGBT community who never felt represented on tv and felt alone and different," she wrote.