Supergirl's James "Jimmy" Olsen (played by Mehcad Brooks) will take on the DC superhero identity of the Guardian.
"James is going to decide that he can no longer sit back and be a sidekick, so he’s going to decide to become a vigilante, and he’s going to become Guardian, complete with the shield," said Supergirl executive producer Andrew Kreisberg (via IGN).
Originally created in 1942 by Joe Simon and Jack Kirby for DC's Star-Spangled Comics, the character has been used intermittently since then by the publisher. One of the fictional characters behind the Guardian comic book identity has appeared previously in Supergirl. Eddie McClintock played James Harper in a first season episode, but never assumed the Guardian identity as he did in comic books.
Of course in comic books, Olsen has become a superhero on several occassions - as Elastic Lad, Flamebird, and even Mr. Action.
Olsen's assumption of the Guardian role in Supergirl will serve as a source of conflict for Supergirl and Olsen, who are romantically involved on the show. Olsen's new superhero career "is going to cause a massive problem in his relationship with Kara."
"Now there’s this new masked vigilante, and she has her own feelings about vigilantes, and it becomes a push and pull about who gets to decide who gets to be a hero," Kreisberg said.
Kreisberg and the CW haven't specified which episode of Supergirl that Olsen will first become the Guardian.