Martin Walker (White House Down)

Martin Walker is the primary antagonist of White House Down and the corrupted head of Presidential Detail.

Biography
A man disguised as a janitor sets off a bomb at the center of the US Capitol building. Raphelson, who was in the Capitol, remains unharmed and is taken to an underground command center with Finnerty, while Vice President of the United States Alvin Hammond (Michael Murphy) is taken aboard Air Force One. The White House is put on lockdown, separating Cale from Emily, who had left the tour group to use the restroom. Meanwhile, mercenaries led by Emil Stenz (Jason Clarke), who had disguised themselves as video technicians to get inside the White House, start killing off most of the Secret Service and take the tour group hostage, but Cale manages to take a gun and escape to go find his daughter. Retiring Head of the Presidential Detail Martin Walker (James Woods) escorts the President and his detail to the Presidential Emergency Operations Center. Once Sawyer gains access, Walker kills his detail, revealing himself to be the real leader and wants vengeance against Sawyer after a botched black ops mission resulted in the death of Walker's son. Cale, who failed to find Emily, kills a mercenary and takes his gun and radio. Overhearing the radio, Cale locates and rescues Sawyer.

Walker and Stenz bring in Skip Tyler (Jimmi Simpson) to hack into their defense system, but they still require Sawyer to activate the nuclear football. They locate the remaining chain of command and execute the Secretary of Defense before putting them with the hostages. Emily, while hiding, records a video of the mercenaries and puts in on YouTube before eventually being captured. Cale and Sawyer manage to reach out to the command structure through a satellite phone Sawyer keeps to communicate with his wife and they tell Cale to get the President out through underground tunnels. At the command center, Finnerty uses Emily's video to discover the mercenaries' identities, who used to work for various government agencies. They also discover that Walker has an inoperable tumor, suggesting his involvement to be a suicide mission and that the attack is meant for more dangerous reasons. Cale and Sawyer find the tunnel gate rigged with an explosive and are forced to escape with a presidential limo. After giving chase with Stenz on the White House lawn, Cale and Sawyer get flipped into the White House pool after Cale gets distracted by a mercenary holding Emily at gunpoint. A gunfight erupts which results in an explosion that leaves Sawyer and Cale presumed dead. Hammond is then sworn in as acting President.

When Cale and Sawyer reveal they are still alive, they learn Hammond has ordered an aerial incursion to take back the White House. Knowing the mercenaries have Javelins, Cale tries but fails to stop them from shooting down the choppers. Cale gets into a fight with Stenz and ends up dropping his White House passes for himself and Emily while escaping. Having already learned of Emily from the video, Stenz, now knowing she is Cale's daughter, takes her to Walker in the Oval Office. Meanwhile, Tyler finally finishes the upload into NORAD and launches a missile at Air Force One, killing Hammond and everyone on board. Raphelson is then sworn in as acting President and reluctantly orders an air strike on the White House, which Cale is informed of.

Walker tells Cale over the White House intercom to surrender Sawyer or he will kill Emily. Sawyer ultimately surrenders himself to save Emily. However, he refuses to activate the football. When Walker threatens to kill Emily again, the alarms and sprinklers are set off by Cale setting various rooms on fire. Tyler is killed trying to escape by the bomb on the tunnel gate having been tampered with so it goes off rather than disarm when he leaves. After killing most of the remaining mercenaries and freeing the hostages, Cale is confronted by Stenz, who is ultimately killed by a grenade belt. Sawyer attacks a distracted Walker, who ultimately gains the upper hand and uses him to activate the football before supposedly shooting him dead. Using updated launch codes received by an anonymous source, Walker targets various cities in the Middle East, but before he initiates the launch, Cale crashes into the office in a Presidental escort vehicle and kills Walker with a minigun at the last second. When Emily is told of the air strike, she takes a presidential flag and waves it on the front lawn to get the fighters to call off the attack, which they eventually do. Sawyer is revealed to be alive as the bullet hit a pocket watch handed down to him from Abraham Lincoln. Finnerty calls them to reveal that the mercenaries were not called in by Walker and that there is another mastermind behind the attack. Cale realizes who it is and asks Sawyer for his help in exposing the traitor.

When Finnerty arrives at the White House with Raphelson, Cale tells them Sawyer was killed. Raphelson then orders troops to be placed back into the Middle East, which would go against Sawyer's peace treaty. Cale reveals Raphelson had orchestrated the attack as Walker had received the codes on his pager from him, all because Raphelson was not entirely in agreement with Sawyer's treaty and proves it by having Finnerty call the call-back number on the pager. Sawyer then reveals himself and has Raphelson taken into custody, treating his taking of the Presidency as a coup d'état.