Created by executive producers Greg Berlanti, Ali Adler, and Andrew Kreisberg, the character was introduced in the pilot episode as the elder adoptive sister of protagonist Kara Danvers / Supergirl.

Alex is a bioengineer, physician, scientist and a field agent of the DEO, a secret government agency that works to protect the Earth from extraterrestrial threats.

Alex is also featured in the show's digital tie-in comic book series, Adventures of Supergirl, as well as the 2017 four-part Arrowverse crossover event "Crisis on Earth-X", with Leigh reprising her role across The Flash, Arrow, and Legends of Tomorrow.

[1][2][3][4] At some point, Kara took a reluctant Alex flying through the night and they were spotted by the Department of Extranormal Operations (DEO), a secret government agency tasked with monitoring alien presence on Earth.

Suffering the loss of her father and her suppressed homosexuality, among other factors, caused Alex to excessively drink and party as a young adult.

[10][11] While continuing her work at the DEO, Alex crosses paths with National City Science Police officer Detective Maggie Sawyer.

In the aftermath of the breakup, Kara invites Alex to her friend Barry Allen's wedding on Earth-1, where she ends up having a one-night stand with Legends of Tomorrow's Sara Lance (Caity Lotz), both are soon forced to fight off an invasion of Nazis from a parallel Earth together.

[18] United States Marine Corps colonel Lauren Haley is brought in by the president to supervise Alex,[19] and is determined to discover Supergirl's civilian identity.

[26] After receiving news that her father died, Alex is reluctant to attend his funeral and uses the Obsidian lens to do a Supergirl fantasy that starts to affect her alongside the others that indulge in it.

Following Xotar's arrest and the attack on Flash who has no memory of Joe West's death, Alex receives the information they learned about Despero which is now in her files.

[33] Alex did talk to Allegra Garcia and Chester P. Runk about their failed relationship which they noted after a disastrous fight with the Legion of Doom.

As Barry Allen works to undo the Reverse-Flashpoint at the cost of the Armageddon that Despero foresaw, Sentinel and Ryan Choi as Atom helped Frost and Chillblaine defeat Damien Darhk.

[34] In February 2015, actress Chyler Leigh was cast as Alexandra "Alex" Danvers, initially described as Kara's "confident foster sister whose fascination with her sibling's powers inspired her to become a doctor.

[38] Alex Danvers has no inherent superhuman powers;[39] rather, she is highly intelligent, trained in various forms of martial arts, and has been shown to capably wield any weapon.

[40] She is also an excellent physician and bio-engineer, and has furthermore extensive expertise in marksmanship, hand-to-hand combat,[41] and extraterrestrial physiology,[1] besides being a far-reaching skilled scientist and military tactician.

In addition to that, she has magnetic gloves now which allow her to retrieve any dropped weapon, and her Maaldorian laser pistol that she has taken away from a deceased alien during a rescue mission on Maaldoria was also upgraded and can shoot Kryptonite bullets now.

"[50] Estelle Tang of Elle described Alex's coming-out journey as "nuanced, remarkably moving, and believable reckoning of an adult woman coming to terms with something she had never consciously known about herself.