Martin Christopher Keamy , often simply referred to by his surname as Keamy,, was the head of Charles Widmore's mercenary team. A former marine turned mercenary warlord with no moral qualms, he was hired by Widmore to lead his team aboard the Kahana freighter and arrive on the island; his duties were to apprehend Benjamin Linus, kill any Oceanic Flight 815 survivors, and then "torch the island". During his mission, he/his team murdered Danielle Rousseau, and while holding her hostage, he murdered Ben's adoptive daughter Alex Rousseau right in front of him.
After the rest of his team is killed by the survivors and others, Keamy heads off to the The Orchid to confront Ben and John Locke. Keamy explicitly warned Ben that he had a dead man's trigger strapped to his body that, if it failed to detect his heart rate, would trigger a bomb aboard the freighter automatically and kill everyone aboard it. Enraged over his daughter's death, Ben wasn't deterred from stabbing him to death; the dead man's trigger went off, but thanks to the efforts of Michael Dawson and Desmond Hume, the detonation was delayed. It could not be delayed indefinitely, however, and it activated, triggering hundreds of pounds of C4; while Dawson's efforts allowed many of the freighter's inhabitants to escape, he himself and anyone else on board were killed as the freighter detonated.
Later, Ben saw a vision of Keamy killing Alex when he was judged by the smoke monster. In the flash sideways world, Keamy was a loanshark and hitman who assaulted Sayid Jarrah's brother Omer after he was late on payment, and kidnapped and attempted to assassinate Jin-Soo Kwon on behalf of Sun-Hwa Kwon's father, but he was killed by Sayid before he could kill Jin.
Before the freighter
Keamy was from Las Vegas, Nevada. ("The Constant") According to Ben, Keamy served as a first sergeant in the United States Marine Corps from 1996 to 2001. He later worked for several mercenary companies, including in Uganda, where it was implied (by Ben) he committed war crimes or comparable atrocities. ("The Shape of Things to Come")
On the Island/freighter: Days 94-100 (Season 4)
Keamy, Omar, and other members of the crew were skeet-shooting with automatic weapons. When Michael Dawson, under the alias Kevin Johnson, questioned the "rescue" crew's possession of the weapons, Keamy snidely asked if Kevin had something to clean up. This seemed to be the final straw in Michael deciding to set off the bomb. ("Meet Kevin Johnson")
Keamy introduces himself and Omar to Desmond. ("The Constant")
Upon Frank, Sayid, and Desmond's arrival on the freighter, Desmond began screaming and acting erratically. Keamy questioned Frank on why he brought the two with him. He and Omar then escorted Desmond down to the sickbay, summoning the ship's doctor and locking Desmond in with Minkowski. Later, Keamy and Omar returned to sickbay having been called by the doctor's emergency alarm. The pair quickly subdued Frank, Sayid, and Desmond, taking the satellite phone from Desmond and once again locking Sayid and Desmond in the sickbay. They then took Frank to speak with the captain. ("The Constant")
As Keamy left the freighter's interior, he encountered Frank bringing something into the ship. He reminded Frank not to be late. ("Ji Yeon")
Keamy talks to Ben and threatens to kill Alex. ("The Shape of Things to Come")
He and the other mercenaries were responsible for shooting Karl and Danielle. ("Meet Kevin Johnson") He then took Alex as bait for Ben, in order to extract Ben from his house. However, Ben remained steadfast, denouncing his daughter. Keamy then shot Alex in the head, killing her. This prompted a shocked Ben to unleash the Monster, which attacked the Freighter's mercenaries. Keamy could be heard repeatedly calling for his squad to fall-back. ("The Shape of Things to Come")
Keamy then appeared unharmed, with the rest of the mercenaries behind him, searching for any survivors. He then encountered Frank, who insisted that they return to the helicopter before night. Keamy reluctantly agreed, almost discovering Miles, Sawyer, and Claire in the bushes nearby due to a cry from Aaron. ("Something Nice Back Home")
Keamy attempts to kill Michael, after learning the truth. ("Cabin Fever")
Frank flew Keamy and the rest of the mercenaries back to the Kahana in the helicopter. There, Keamy threatened Captain Gault with a gun, believing that Gault had told Ben about Keamy's history; Gault told Keamy that it was actually Michael who gave him up to Ben. Keamy confronted Michael and attempted to shoot him twice, but his gun failed to fire both times. Keamy let Michael live after he learned that Michael is the only one able to repair the ship's engines. He does, however, knock him unconscious.
Some time later, Keamy confronted Gault and forcibly took his key. Keamy used the key to unlock a safe, from which he took out a folder that contains, in his own words, "secondary protocol." Keamy claimed that this folder would allow him to find Ben, insinuating that Charles Widmore knew where Ben would go. Keamy asked Gault to fix his gun, and left the room.
Keamy shows the device to Gault. ("Cabin Fever")
Keamy began making preparations to return to the Island. He ordered Frank to refuel the helicopter, and Omar helped to attach an elaborate device to Keamy's arm. That night, Keamy and the other mercenaries suited up, gathered their weapons, and prepared to board the helicopter. Frank refused to fly them, believing that Keamy planned to kill everyone on the Island. Keamy threatened to kill Frank, but instead he killed Doc Ray by slitting his throat. Frank remained resolute, and Keamy threatened to shed more innocent blood. At that moment, Captain Gault--armed with a pistol--and two other men arrived.
Keamy meets a surrendered Ben face-to-face for the first time. ("There's No Place Like Home, Part 1")
Gault held Keamy at gunpoint and demanded that the mercenaries surrender, but he paused when Keamy showed him the device on his arm. While Gault was distracted, Keamy shot him in the heart, killing him. Frank, having seen enough violence, agreed to fly Keamy and his crew to the Island. ("Cabin Fever")
Upon arriving on the island, Keamy and the other mercenaries handcuffed Frank to a seat in the helicopter to ensure that he did not escape and leave them behind. They then continued on to The Orchid. Upon arrival, they silently paced and waited for Ben's arrival. When Ben did arrive, he surrendered to Keamy. Keamy then put his pistol to Ben's head, seemingly ready to kill him. Ben did not flinch, but simply looked at the barrel. Keamy then knocked Ben out with the butt of the pistol. ("There's No Place Like Home, Part 1")
Keamy and his team are under attack by the Others. ("There's No Place Like Home, Part 2")
Keamy and his men returned to the helicopter with Ben. When they were there they encountered Kate who claimed to be being chased by the Others. Keamy sent men into the jungle who were promptly disabled. A firefight ensued during which Keamy's men were killed. Keamy chased after Ben and Kate, who ran into the jungle. As he was doing so Sayid tackled him and the two fought. After being stabbed by Sayid in the back, Keamy managed to pin him to the ground and was choking him with a branch when he was shot, apparently fatally, by Richard.
Keamy, in his final minutes of life, taunts Ben. ("There's No Place Like Home, Part 2")
Later, however, Keamy arrived at the Orchid and revealed that he had a bulletproof vest that absorbed most of the bullet force. Keamy then proceeded to taunt Ben about how he killed Alex when Locke emerged. He said he had no quarrel with Keamy. While Locke had Keamy distracted with conversation, Ben emerged and disarmed Keamy by hitting him three times with the telescopic baton, then Ben grabbed Keamy's own knife and stabbed him to death. Before dying, he said that Charles Widmore would never stop looking for Ben or the Island. Keamy's death caused the dead-man switch on his arm to activate, which triggered the massive explosion on the Kahana — causing it to sink, and presumably killing everyone that remained on the freighter, except Jin, who was thrown into the water with the force of the explosion. ("There's No Place Like Home, Part 2")
Keamy's image inside the monster. ("Dead Is Dead")
In the flash sideways, Keamy loaned money to Omer, Sayid Jarrah's brother, so that Omer would be able to open a second dry cleaning business. Although Omer payed him back in full, Keamy later extorted "security" interest from him. ("Sundown")
In exchange for a Rolex watch and $25,000, Keamy was hired by Mr. Paik to kill Jin for having a sexual relationship with Mr. Paik's daughter Sun. Paik sent Jin to Los Angeles to deliver the watch and money to Keamy. ("The Package")
The money Keamy was due to receive from Jin was confiscated by customs at the airport. Keamy arrived at Jin's hotel to collect his reward and was disappointed to find that the money was missing. Sun, who traveled to L.A. with Jin, promised to pay Keamy with money out of her own bank account. While Sun went to get the money, Keamy took Jin to a restaurant he has access to and tied him up in a walk-in freezer. Knowing that Jin was incapable of understanding him, Keamy spoke aloud to Jin of his intention to kill him at Mr. Paik's orders. ("The Package")
Keamy speaks to a confused Jin. ("The Package")
Meanwhile, Keamy sent Omar, one of his henchmen, to capture Sayid and bring him to the restaurant. When Sayid arrived, Keamy explained to Sayid that he wanted Omer's loan repaid. He made threats against Omer's family unless Sayid took care of the situation. At that point, Sayid grabbed Omar and successfully used him as a human shield against gunfire from Keamy's thugs. Sayid then used Omar's gun to shoot the rest of the henchman. Realizing that he was at a disadvantage, Keamy told Sayid that he would forgive the debt and allow Sayid to walk away. Sayid replied, "I can't." and shot Keamy in the chest. ("Sundown")
Keamy offers Sayid eggs. ("Sundown")
Keamy was still alive, though critically wounded, when Sun and Mikhail Bakunin arrived at the restaurant. Keamy noticed Jin, who had escaped from the freezer, creep behind Mikhail with a gun pointed at Mikhail's head. As Mikhail was unaware of this, Keamy mumbled at him to turn around. Mikhail did so and, after a brief scuffle, was shot by Jin in the eye. ("The Package") Keamy's injury was fatal, and he died shortly after Mikhail's arrival. Sayid would be arrested for his role in the deaths of Keamy and his associates. ("The Last Recruit") It is unknown what became of Keamy after this point.
- Keamy's episode count is 12, his two final appearances were made by his flash-sideways counterpart.
- The five-toed paw tattoo on Keamy's right shoulder vaguely resembles the company logo of Blackwater Worldwide, a privately-owned Tactical Training & Contract Security Service organization headquartered in North Carolina, USA.
- Kevin Durand also had these same visible tattoos when he guest starred on one episode of the TV series "Shark", suggesting that they are the actor's (as well as the characters').
- Keamy and Gault seemed to know each other fairly well, given that Gault referred to him by his first name.
- Initial casting requirements for this role in "The Constant", described Martin Keamy as "late 20s - 30s, any ethnicity, dangerous, physical - a great tactician, loyal friend and the last enemy you ever want. Military type. Follows orders and doesn't question them". 
- Out of the main cast of characters, Keamy had only met Michael, Miles, Sayid, Desmond, Ben, Kate, Locke, Daniel, Charlotte, Lapidus, Jin and Sun.
- Sawyer & Locke (the latter: prior to meeting him a few days later ("There's No Place Like Home, Part 2") viewed him from the cover of Ben's house when holding Alex hostage. ("The Shape of Things to Come")
- Claire saw him while hiding in the jungle. ("Something Nice Back Home")
- Hurley saw him at the Orchid while hiding in the jungle. ("There's No Place Like Home, Part 1")
- Keamy probably met Charlotte and Faraday on the boat.
- Keamy was aware that it was Richard who shot him. ("There's No Place Like Home, Parts 2 & 3")
- He met Jin and Sun in the alternate timeline. ("The Package")
- Out of all the characters who have not met Jack, Keamy has had the most appearances.
- Martin is one of 8 supporting characters to have their name appear in a soundtrack title.
- Witnesses of death: John Locke, Benjamin Linus
- Last words: "Wherever you go... Widmore... Will find you...."
- Jonn Keamy, a family friend of Carlton Cuse, coached Carlton's son Conor in baseball. John and his son Christian still gather with the Cuse family for events such as dinners, Dodger Games, yoga, movies, and the occasional party, and the sons now play competitive high school baseball together. [source needed]
- The name Martin comes from the Latin Martinus, which means "Servant of Mars" or "Servant of War".
- In Mayan Astrology, the sign KIMI, pronounced the same way as Martin's last name, means DEATH.
- For fan theories about these unanswered questions, see: Martin Keamy/Theories
- What did Keamy do in Uganda that was significant enough for Ben to make note of it?
- Keamy's Paradise - Meme fansite based on Keamy