'The Flash': Who Plays Jaco Birch?

Iris West-Allen (Candice Patton) suited up as a speedster in tonight's episode of The Flash -- and faced off against a familiar face in the process.

Mild spoilers for tonight's episode of The Flash, "Run Iris, Run", below!

Tonight's episode saw Team Flash dealing with Matthew Kim/Melting Pot (Leonardo Nam), a metahuman with the ability to switch people's DNA. While this largely caused a problem for Barry (Grant Gustin) and Iris, it also unintentionally created another new metahuman, with [META'S NAME] fire-related powers being transferred over to someone else.

Eventually, Iris discovered who those powers had been traded over to: Jaco Birch (Max Adler), a heavy-metal rock fan.

For those who keep up with TV -- or who followed Gustin from his previous television roles -- Adler is a pretty familiar face. The actor most notably had a role on Glee, playing David Karofsky for five seasons of the show.

Karofsky served as a bully for the kids at William McKinley High School, only for it to be revealed that he was secretly repressing his sexuality. Over the course of Glee's tenure, Karofsky came to terms with the fact that he was gay, with Adler's performance resonating with quite a few Glee fans in the process.

Outside of his role on Glee, Adler is known for his television roles on Switched at Birth, Chuck, and The Big Bang Theory. He also has made appearances in films like Sully, Believe Me, and Cafe Society.

Adler is just the latest actor to make the jump from Glee to the Arrowverse, but the nature of his appearance is sure to intrigue fans of both franchises. For one thing, both Adler and Gustin's Glee characters were sort of in the same orbit of the show, with Karofsky even briefly (and awkwardly) hitting on Sebastian during one scene. Whether or not the two will reunite at some point throughout tonight's episode remains to be seen.

The Flash airs Tuesdays at 8/7c on The CW.