He will guest-star in the 10th episode of The CW drama's second season.

Arrow is adding a dangerous new villain.

Firefly alum Sean Maher is joining season two of The CW's comic book drama, The Hollywood Reporter has learned exclusively.

Set to appear in the 10th episode, Maher will guest-star as the evil Mark Scheffer, better known as DC Comics supervillain Shrapnel, a serial bomber who places Starling City in the grips of terror and threatens the life of Sebastian Blood (Kevin Alejandro).

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In the DC Comics universe, Shrapnel's backstory isn't fully known, though it has been established that he was at one point married with two daughters. Made of metal, Shrapnel's powers are superhuman strength and stamina.

The casting comes as Arrow continues to dig into the DC Comics vault, featuring comic book characters like Black Canary, Bronze Tiger, Flash, Sin, Isabel Rochev and Sebastian Blood over the course of the season. It also marks the latest Firefly alum to join the series, with Summer Glau previously cast in a recurring role.

Maher is repped by Principal Entertainment. He is best-known as Simon Tam on Joss Whedon's Firefly and Serenity. Other credits include Make It or Break It, the short-lived The Playboy Club and Whedon's big-screen adaptation of Much Ado About Nothing.

Arrow airs Wednesdays at 8 p.m. on The CW.

E-mail: Philiana.Ng@THR.com

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