Leigh and Harewood will be featured as series regulars. Here's a breakdown of their characters, per TheWrap:
Harewood ("Homeland," "Selfie") will play Hank Henshaw, a former CIA agent who heads up the Department of Extra-Normal Operations and tracks extraterrestrial threats. In DC Comics lore, he eventually becomes Cyborg Superman. Leigh, meanwhile, ("Grey's Anatomy," "That '80s Show") plays Kara's/Supergirl's (Melissa Benoist) foster sister Alexandra "Alex" Danvers, described as a confident doctor who became fascinated by her sibling's powers at a young age.
Those two are just the latest to sign up for "Supergirl," with Calista Flockhart also joining the cast this week. Laura Benanti and Mehcad Brooks also star.
TheWrap also reports that Andrew Kreisberg, who worked on fellow DC Comics properties "Arrow" and "The Flash" for The CW,