The 32-year-old actress will be a series regular and the main baddie for the upcoming third season. Reign is a Worldkiller, a biological weapon, bloodthirsty, super-powerful monster, created on Krypton by Zoe-El. In the comics, she tries to take Supergirl down and conquer Earth. The TV version of the character will have a different costume than the comic book version.
"Greg [Berlanti] and I have wanted to work with Odette for years," executive producer Andrew Kreisberg said in a statement. "We are beyond excited to have her join our cast in the scary, powerful and heartbreaking role of Reign."
The first two seasons of Supergirl featured an impressive list of guest stars, including Wonder Woman star Lynda Carter as the female president, Tyler Hoechlin as Superman, former Lois Lane, Teri Hatcher, as villain Rhea, Dean Cain, Helen Slater and Kevin Sorbo.
Supergirl returns this fall on The CW. For more on the superhero series, watch below.