Supergirl is set to become the first live-action television series to include a transgender superhero.
Nicole Maines, a transgender actor and activist, will join the upcoming fourth season of the Warner Brothers drama as Nia Nal, who becomes known as Dreamer.
The character is described as a “soulful young transgender woman” with a “fierce drive to protect others”.
She added: "I want fans to take away an understanding of trans people. We can be anybody, we can be who we want, we can be superheroes - because in many ways we are."
Maines had already made headlines in June 2013 when the Supreme Court in the US state of Maine ruled that her rights had been violated when she was refused access to the female toilet in her high school.
Supergirl is based on the DC Comics character of the same name and is set in the same universe as other comic book characters such as The Flash and Arrow.
Maines said she is keen for viewers to understand trans character's plotline does not have to be centred around them being trans.
"Nia is so much more than just a trans superhero. She is a reporter, she is hopeful, she's powerful, wise and such a good friend,” she said.
Maines - who won a 2016 GLAAD award for her performance in US show Royal Pains - was previously featured on the HBO documentary The Trans List. She also the subject of the book, Becoming Nicole, by Amy Ellis Nutt.
Fans celebrated the announcement on Twitter - with one saying Maines was "already a superhero".
The news Supergirl plans to introduce a transgender superhero comes days after the announcement that a Batwoman TV series will be created.
Like the comic book character, she will be a lesbian, meaning she will become the first lesbian superhero at the centre of a television series.
Batwoman was introduced in the 1950s as a love interest for Batman to banish rumours of his own homosexuality.
In 2006, the character was reintroduced as a gay woman called Kate Kane and has since become the highest profile openly gay character of any DC comic.