Eddie McClintock, who has appeared on shows like Warehouse 13, Bones, and Marvel's Agents of S.H.I.E.L.D., will head to Supergirl next week in the role of Colonel James Harper.
In the comics, of course, James Harper is the superhero Guardian, a creation of Jack Kirby and Joe Simon who is closely tied to the Cadmus Project, the Newsboy Legion, and Jimmy Olsen.
Harper, a former Metropolis police officer, took on the name of the Guardian and was in some ways DC's version of Captain America -- a man with peak human abilities, a blue costume, and an indestructible shield.
After his retirement, Harper was cloned, along with the Newsboy Legion; the elder Newsboys remained on as scientists at Cadmus, where the younger Harper served as chief of security and wrangled the kids as the original Harper had with the original Newsboys.
Cadmus has been name-dropped on Arrow, and a vial from Cadmus Labs has been hidden in plain sight since the pilot of The Flash, but the lab has never really served a significant purpose on any of the current crop of DC TV series. For his part, Guardian was one of a number of DC characters speculated by fans to be the costumed identity of John Diggle on Arrow.
While the episode, titled "Manhunter," will feature a number of minor characters in military roles, a recognizable face like McClintock's seems an unlikely candidate to be a one-off. Then again, they did have a Buffy the Vampire Slayer veteran as Cameron Chase, just that one time.