|Nationality:||United States of America|
|Affiliation:||NYPD (formerly) Federal Air Marshal Service|
|Profession:||Federal Air Marshal|
|Played by:||Liam Neeson|
Bill Marks is an alcoholic U.S. federal air marshal; he enrolled in the Air Marshal service after he was discharged from the NYPD. On a non-stop flight from New York to London aboard British Aqualantic Flight 10, midway over the Atlantic Ocean, Marks receives text messages on his secure phone stating that someone on the plane will die every 20 minutes unless $150 million is transferred into a specific bank account.
Breaking protocol, Marks consults with Jack Hammond, the other air marshal on the flight. Hammond is revealed to be smuggling cocaine in a briefcase; following an altercation, Marks ends up killing him in a lavatory. This occurs exactly at the 20 minute mark, resulting in the first death. As Marks attempts to stall for time with the texter, he works with Nancy Hoffman, a flight attendant, and Jen Summers, a passenger seated next to Marks, to discover the texter's identity. When the next 20 minutes expires, the captain suddenly dies of poisoning.
The public becomes convinced that Marks is hijacking the plane, as the bank account is in his name and a passenger uploads video footage of him treating passengers aggressively with no explanation. Co-pilot Kyle Rice has been instructed by the TSA to ignore Marks and land in Iceland, the closest destination; he diverts the plane but continues to cautiously trust Marks. Cell phone programmer Zack White is asked by Marks to design a hack which will cause the texter's cell phone to ring. It is discovered in the pocket of a passenger, who claims to have never seen the phone before. Following a fight with Marks, the passenger dies in a similar fashion to the captain.
In the lavatory, Marks finds a hole in the wall that allowed someone to shoot a poison dart at the captain; he finds that the deceased passenger was struck with a dart as well. While Marks and Summers try to gain access to the texter's phone, it suddenly activates, sending automated messages to TSA implying that Marks is suicidal and is going to detonate a bomb on the plane.
Marks finds the bomb hidden in the cocaine smuggled by Hammond. Passengers attempt to disable Marks, convinced he is a terrorist. They overpower Marks but passenger Tom Bowen uses Marks's gun to make them move away. Marks finally explains the situation and they agree to work with him.
Unable to land the plane in time, he attempts to initiate a protocol of least damage: by descending the plane to 8,000 feet to equalize air pressure, placing the bomb in the rear of the plane, covering it with baggage and moving the passengers to the front to contain the explosion and minimize casualties.
Watching a video clip of himself handling passengers, Marks notices Bowen—whom he had initially cleared of any suspicion—slipping the texter's phone into the pocket of the second poison victim. Realizing that Bowen is the culprit, he learns that Bowen's father was killed in the 9/11 terrorist attacks and that he and White are ex-military. Appalled by the lack of security at U.S. airports after 9/11, Bowen believes framing an air marshal as a terrorist will lead to drastically increased security. Bowen is prepared to die with the plane and shoots White, who planned to parachute off with the money, after Marks persuaded White to disarm the bomb. Following another fight, Marks shoots Bowen in the head. Marks then fights and defeats White, who survived being shot by Bowen. Immediately afterwards, he escapes from the blast radius of the bomb; White is killed by the subsequent detonation.
Rice manages an emergency crash-landing at an air base in Iceland after the bomb explodes, disregarding orders from his fighter-jet escort. Despite their warnings, the fighter jets do not shoot the airliner down. The plane is damaged in the landing, but no one else dies. Marks is hailed as a hero in the media, and he and Summers begin their friendship.
Bill Marks carried a SIG-Sauer P226 Elite Stainless pistol in unknown caliber with red wood grips and bright finish. The Air Marshal service carries the SIG-Sauer P229 in .357 SIG, not the P226. However, the NYPD is allowed to carry the P226, so Marks may have just carried the pistol over from the NYPD to the Air Marshal service.