The Emerald Crusader already has his love interest, Blake Lively, and now he's got an adversary for his big screen debut.  Peter Sarsgaard is joining the cast of Martin Campbell's "Green Lantern" as the evil Dr. Hector Hammond.

The disappointing son of a U.S. senator, Hammond gains telepathic and telekinetic abilities after he discovers a mysterious meteor.  Ryan Reynolds is already on board as Hal Jordan, a test pilot who finds a dying alien who bestows the ring of the Green Lantern Corps, making him the new guardian of Earth's sector.

Blake Lively was cast as Reynold's love interest, Carol Ferris, last week.

The acclaimed Sarsgaard recently completed production on "Knight and Day" opposite Tom Cruise and Cameron Diaz.  He's currently shooting the indie "The Ledge" with Terrence Howard and Evan Rachel Wood, but can be seen in theaters in the Oscar contender "An Education."  He's best known for his roles in "The Skeleton Key," "Jarhead" and "Kinsey."

According to the Hollywood Reporter, production should begin this March in New Orleans.