Casting continues for The Flash, which has cast the other half of Firestorm, Dr. Martin Stein, and openly gay villain Pied Piper.

Alias alum Victor Garber will play Dr. Martin Stein, “a brilliant but arrogant nuclear physicist who has sacrificed everything, including a marriage, for his work in transmutation.” The S.T.A.R. Labs particle accelerator malfunction “fused him with the younger, more impulsive Ronnie Raymond,” so “he races to find a way to separate the two before it’s too late.”

He will debut in the 12th episode of the season.

A few of Garber’s numerous other roles include Web Therapy, Power, Eli Stone, Argo, and the upcoming Selfless.

The Flash has also tapped Smash alum Andy Mientus for a multi-episode arc as Hartley Rathaway, who becomes the villain and member of the Rogues Pied Piper. He is slated to appear in the 11th and 12th episodes of the season.

He is described as “a genius who used to work at S.T.A.R. Labs until he had a falling out with the mysterious Dr. Harrison Wells, the brains and money behind the particle accelerator.” After the particle accelerator malfunction, “Hartley lost his hearing but started creating sonic weapons that he uses to destroy Harrison’s latest creation: The Flash.”

According to TVLine, the series will not be shying away from Hartley’s sexuality.

Mientus’s other roles include Anger Management and Chasing Life.

Garber and Mientus join a cast that has recently added Amanda Pays (Tina McGee), Dominic Purcell (Heatwave), Greg Finley (Girder), Clancy Brown (General Wade Eiling), Kelly Frye (Plastique), Wentworth Miller (Captain Cold), and Robbie Amell (Ronnie Raymond).

The Flash stars Grant Gustin (Barry Allen), Jesse L. Martin (Joe West), Candice Patton (Iris West), Tom Cavanagh (Harrison Wells), Danielle Panabaker (Caitlin Snow), Carlos Valdes (Cisco Ramon), Rick Cosnett (Eddie Thawne), and John Wesley Shipp (Henry Allen).

The Flash debuted this week to a towering massive 4.8 million viewers, the highest rated premiere for a CW series since 2009.

The Flash airs Tuesdays at 8:00 p.m. ET on The CW.