'Supergirl': Who Is Agent Liberty?

Supergirl returns tonight for its fourth season and with it comes a new threat unlike anything the Girl of Steel has faced before.

Spoilers for tonight's Season 4 premiere of Supergirl, "American Alien", below.

Tonight's episode introduced audiences to Agent Liberty (Sam Witwer), the mysterious figure apparently behind the anti-alien Earth First movement that proves to be a major threat for not just Supergirl, but all of the aliens living on Earth.

Supergirl's version of Agent Liberty is the ruthless and terrifying leader of the Children of Liberty, a human-first hate group. While the character is described as "a brilliant orator in the guise of a family man" who can easily convince people that he's right, he's seen only in his Agent Liberty costume in tonight's episode -- a costume that obscures his face behind a rigid mask. Even with the mask obscuring his physical face, Agent Liberty's true colors shine through, though. He's teamed up with Mercy and Otis Graves (Rhona Mitra and Robert Baker) to carry out vicious acts all as part of the "Earth First" movement.

For DC fans, Supergirl's take on Agent Liberty may be a surprising one. First debuting in 1991, the comics version of Agent Liberty, real name Benjamin Lockwood, is an ex-CIA agent who becomes disenchanted with the government. It leads him to join the paramilitary group the Sons of Liberty. Initially, Agent Liberty's work with the group to overturn the government brings him into conflict with Superman, but when the Sons ask him to assassinate a politician, he refuses and leaves the group. Agent Liberty later becomes so disenchanted with the group that he helps bring down the Sons, giving important information to Clark Kent. In the comics, he also helps the Justice League from time to time and is, ultimately, a hero.

While Supergirl's version of Agent Liberty appears to be drastically different from his comic book counterpart, they may more readily recognize the actor behind the role. Sam Witwer previously appeared on Smallville as Davis Bloome/Doomsday, memorably appearing through the show's eight season. His appearance this season on Supergirl makes him just the latest Smallville alumni to appear on the series, following Laura Vandervoort and Erica Durance.

"We love it, and we think the fans love it," showrunner Robert Rovner said of the show's legacy casting last year. "We love seeing people that we know and are familiar with step into other roles. And what's great about them is that they're all wonderful actors as well. So, you get the excitement of seeing them in the new role, but they also bring a lot when they take on these new characters."

What do you think about Supergirl's Agent Liberty? Let us know your thoughts in the comments below.

Supergirl airs Sundays at 8/7c on The CW.