Supergirl Original Character.

Alex Danvers first appeared on the tv series Supergirl as her adoptive sister on earth played by Chyler Leigh, she had a failed relationship with Maggie Sawyer and would later date Jimmy Olsen's sister, Kelly Olsen.

By the end of season three, she'd be made the new director of the DEO after having been an agent for years, she would only resign after Lex took control of the agency in season five. She'd take on the name of Sentinel in season, becoming a hooded vigilante after seeing she had to find a new way. In the final season, she'd marry Kelly and adopt her alien daughter, Esme. Surprisingly Alex never made it into the main canon comics, however she's managed to appear in other shows of the Arrowverse, during the Crisis crossovers, going to Barry & Iris's wedding. She'd also be a recurring character in The Flash season eight consulting the team on the recent alien villain, Despero.