<Li> Joseph Gordon - Levitt as Rexford G. "Rex" Lewis / The Doctor / Cobra Commander The Baroness's brother, a former soldier who was thought to have been killed during a mission led by Duke--instead, he became the disfigured head scientist of Military Armament Research Syndicate (MARS). USA Today reported that Gordon - Levitt would play multiple roles . He wore prosthetic makeup under a mask that was redesigned from the comics because the crew found it too reminiscent of the Ku Klux Klan . Upon seeing concept art of the character, Gordon - Levitt signed on because; "I was like,' I get to be that? You're going to make that (makeup) in real life and stick it on me? Cool . Let me do it .' That's a once - in - lifetime opportunity ." Gordon - Levitt is a friend of Tatum and they co-starred in Stop - Loss and Havoc . His casting provided extra incentive for Tatum to join the film . Gordon - Levitt described his vocal performance as being "half reminiscent" of Chris Latta's voice for the 1980s cartoon, but also half his own ideas, because he felt rendering it fully would sound ridiculous . </Li> <Li> Christopher Eccleston as Laird James McCullen XXIV / Destro A weapons designer and the founder of MARS who is the main villain in the early part of the film . Irish actor David Murray was originally cast as Destro, but was forced to drop out due to visa issues . Murray was later cast as an ancestor of James McCullen in a flashback scene . </Li> <Li> Sienna Miller as Anastasia DeCobray / Ana Lewis / The Baroness The sister of Cobra Commander and a spy . Years earlier, The Baroness was going to marry Duke, but he left her at the altar, due to his guilt over her brother's apparent death . Miller auditioned for the part because it did not involve "having a breakdown or addicted to heroin or dying at the end, something that was just maybe really great fun and that people went to see and actually just had a great time seeing ." Miller prepared with four months of weight training, boxing sessions and learned to fire live ammunition, gaining five pounds of muscle . She sprained her wrist after slipping on a rubber bullet while filming a fight scene with Rachel Nichols . </Li> <Li> Lee Byung - hun as Thomas Arashikage / Storm Shadow Snake Eyes' rival; both were close members of the Arashikage ninja clan . Lee was unfamiliar with G.I. Joe because the franchise is unknown in South Korea, but Sommers and di Bonaventura told him that it was not necessary to watch the cartoons to prepare for the role . Lee was attracted to Storm Shadow's "dual personality," which he stated has "huge pride and honor ." </Li>

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