Not only will the "Manhunter" Episode of Supergirl feature J'onn J'onzz filling Kara in on how he came in contact with Jeremiah Danvers (the returning Dean Cain), but from the synopsis below it sounds like we'll be meeting a small screen take on DC street level vigilante, Guardian - or at least, his alter ego, James "Jim" Harper. This character was a cop in the comics, but the Col. in front of his name suggests he'll be a military man on the show.
J’onn J’onzz reveals the details of meeting Kara and Alex’s father, Dr. Jeremiah Danvers (Dean Cain), and assuming Hank Henshaw’s identity. Also, Kara debates trusting someone new with her secret identity and Siobhan (Italia Ricci) plots against Kara, on SUPERGIRL, Monday, March 21 (8:00-9:00 PM, ET/PT) on the CBS Television Network.
Supergirl stars Melissa Benoist (Kara Danvers/Supergirl), Calista Flockhart (Cat Grant), Chyler Leigh (Alex Danvers), Mehcad Brooks (James Olsen), David Harewood (Hank Henshaw), and Jeremy Jordan (Winslow “Winn” Schott).
Recurring cast appearing in the episode are Jenna Dewan-Tatum (Lucy Lane), Dean Cain (Dr. Jeremiah Danvers), Italia Ricci (Siobhan Smythe), Briana Venskus (Agent Vasquez), Jay Jackson (News Anchor), Malina Weissman (Young Kara), and Jordan Mazarati (Young Alex). Eddie McClintock guest stars as Col. James Harper