Kai Leng

Kai Leng is an assassin working for the human-survivalist organization Cerberus. Leng was formerly a lieutenant and N7 marine in the Systems Alliance known for having anti-alien attitudes. He is described as being Earth-born with features that show his dominant Chinese heritage.

Dossier
While little is known about Kai Leng's early life, Alliance records show that he enlisted in the Alliance Military on November 14, 2172 at the age of 16, although his credentials were faked at the time. Leng's prowess in combat and xenophobic nature drew the attention of the Illusive Man, and Cerberus helped liberate Leng from prison after he was incarcerated for murder. The Illusive Man used Leng as his best wet-work operative and assassin for over a decade, realising he was not only ruthless but discreet and methodical. Leng became the Illusive Man's most trusted agent, working as an infiltrator and assassin. His cybernetic modifications appear to include Cerberus's Phantom-class implants.

Tours of Duty

 * 2172 Terminus Systems Patrol and reconnaissance
 * 2173 Exodus Cluster Patrol and reconnaissance (reprimanded for taking medals from dead enemy officers; sentence was reduced in light of previous, exemplary service record)
 * 2174 Raid of Entiyon (recommended for Systems Alliance Medal of Valor)
 * 2175 Kite's Nest Tactical reconnaissance (accepted into Interplanetary Combatives Academy)
 * 2176 Received N7 designation from Interplanetary Combatives Academy.
 * 2176 Dishonorably discharged and imprisoned for 20 years in an Alliance prison after charge of first-degree murder (while on leave, murdered a krogan in a bar on the Citadel using a standard-issue service blade).

Mass Effect: Foundation 2
Kai Leng worked with agent Rasa on a job that entailed subverting a Shadow Broker agent for Cerberus. Leng contacted Rasa through vidcomm in lieu of the Illusive Man, and informed her of a complication to Cerberus' plans. A bounty hunter named Urdnot Wrex has been hired to take out Rasa's target Fist, and the agent assured him she can handle it. Leng held little confidence in Rasa's plans, claiming that if he took care of someone they stay "taken care" of, and Rasa countered that it's precisely the reason she was on the mission, not him.

Repeatedly asking Rasa how she's going to deal with the complication, Leng then commed her Fist was on the move and with guards, making Rasa realize Leng had been shadowing Fist from afar. Rasa was annoyed at Leng's intrusion, but the assassin countered that there were few opportunities to turn someone working for the Shadow Broker. Leng was there for backup, and Rasa made her resentment at his involvement clear.

An explosion near Fist's residence grabbed both Leng's and Rasa's attention, and the assassin began to get impressed with Rasa's scheming. Rasa unexpectedly cursed and Leng remarked it's not the reaction he was expecting, though Rasa clarified it's because of the discovery from Fist's files: he was bought off by Saren Arterius.

Leng warned her there's no time left when Rasa decided to ask Fist for details herself, but Fist arrived earlier than she expected, sending her hiding. Rasa admonished Leng for not telling her Fist was already in the building, and Leng smugly reminded her that she said she could handle it.

Mass Effect: Foundation 3
A day after Saren Arterius' attack on Eden Prime, Leng captured and interrogated a runaway Alliance soldier regarding what caused the attack. As soon as he was done, he contacted Rasa, who was on the Citadel. The traitorous captive produced nothing they didn't know, and without other leads Leng brainstorms with Rasa for ideas.

Comparing Leng's findings with hers Rasa noted that a Gunnery Chief Ashley Williams was involved in the fighting. Leng assumed that Williams was killed-in-action along with the rest of her squad, only for Rasa to inform him that Williams was alive and on the Citadel. She then asked him what he intended to do with his captive, and Leng answered that he was going to dispose of him. He also warned Rasa to be cautious in interviewing Williams.

At the end of the interview, Rasa informed Leng that geth attacked the colony, though Captain Anderson failed to report that. Apparently, Saren and the geth were after a Prothean Beacon, which came into contact with Commander Shepard. Leng stated that he will report back to the Illusive Man and advised that Rasa do so as well. Rasa insisted that she stay a little while longer to find what happened to Shepard and the beacon, but Leng refused her.

Mass Effect: Foundation 4
Leng visited Rasa in her quarters when the agent failed to appear for her debrief. While Rasa resented his presence as usual, he took a glance at the dossiers the woman had been researching for the Illusive Man, and listened to her grumble about wasted time on Shepard's SSV Normandy companions. Rasa reasoned Cerberus should've focused more on learning about the Commander, not on people with issues, and Leng replied she could've told the Illusive Man so if she hadn't missed the debrief. Leng added he wouldn't recommend it, however, and before leaving reminded her not to miss the next debrief.

Mass Effect: Foundation 5
The assassin chanced upon Rasa concluding her discussion with the Illusive Man and inquired about her new orders. She was told to stay put for the moment and he brought up the subject of Shepard's demise, callously opining everyone's got to die sometime. He figured that if the Commander wasn't strong enough then maybe someone else should take the lead for humanity. Rasa asked if Leng thought he was the one, though he dismissed the idea for the moment as he had a mission to attend to.

It wasn't about the investigation into Shepard's death, as he told Rasa when she asked. Leng got touchy when Rasa determined he was as dark on the matter as she was, bragging about his seniority over her in terms of years in the group. Rasa was uninterested and wondered out loud who the people assigned to Shepard's case were, assuming they must be important enough to replace Leng, though Leng rhetorically questioned who could ever do such a thing.

Mass Effect: Retribution
When Cerberus confirmed Paul Grayson was on Omega, Leng was charged with hunting down and capturing him. Leng and a squad of six other Cerberus operatives capture Grayson. During the mission Leng personally kills Liselle, the daughter of Aria T'Loak and Grayson's lover. He is then ordered to oversee Grayson during the Reaper nanotechnology experiment. It was Leng's idea to dose Grayson with red sand to lower his resistance to the Reaper technology.

The Illusive Man orders Leng to exterminate Grayson if the experiment becomes too dangerous to continue, or if he got out of control. However, when a turian strike team raids the research facility that houses Grayson, Leng chooses to rescue the Illusive Man rather than kill Grayson, meaning Grayson is rescued by the turians. After the assault, the Illusive Man sends Leng to Aria as Cerberus' representative, both to negotiate for her assistance in finding Grayson, and to keep an eye on her.

After bringing the proposals of the Illusive Man to Aria, Leng remains on Omega, closely monitoring Aria's movements and waiting for Grayson to show up. After Grayson arrives on Omega, lured by a distress call from Kahlee Sanders, Leng follows Grayson, but doesn't engage him because of his cybernetic enhancements. He stays out of the way as Grayson tears through Aria's troops and flees to the spaceport.

After Grayson escapes Omega, Kai Leng offers David Anderson and Kahlee Sanders - who are both looking for Grayson - a ride off Omega, in exchange for their help in taking out the Reaper-possessed monster Grayson had become. Knowing he is a Cerberus agent, Anderson and Kahlee attack Leng, but he gets the upper hand and asks again for their help, knowing Kahlee is the key to finding Grayson. They reluctantly accept; however, when confronted with turian security guards near Leng's shuttle, they take their chance. After distracting Leng, Anderson tasers him, then convinces the guards to let him take Leng's limp body. Leng is then tied to the copilot chair with rope from the shuttle's med kit. During the journey, Kahlee realises the Reapers are sending Grayson to the Jon Grissom Academy, home of the Ascension Project.

Upon arrival at the Grissom Academy, both Anderson and Sanders leave the shuttle to protect the biotic pupils at the Project, leaving Leng tightly bound to the chair. After a struggle with the rope that left him bleeding, Leng manages to free himself and get into the Academy. He later encounters a gifted biotic student named Nick, and needing Nick's biotics in lieu of a weapon, manages to persuade Nick that he is on his side.

On his way through the Academy, Leng hears Grayson in the distance, prompting both he and Nick to hide in a nearby empty room. Leng intends to ambush Grayson using Nick's biotics, but when the attempt fails, Leng tries to steal Grayson's weapon. He fails and is almost killed, only to be saved by Anderson, who kills the Reaper-controlled Grayson with a shotgun.

Anderson refuses to simply let Leng escape; however, Nick has been shot and is badly hurt. Anderson has to choose between saving Nick and letting Leng go, eventually choosing to help Nick - though not before shooting Leng in each leg to try and slow him down. Despite his injuries, Leng still manages to get back to the shuttle and escape. He is able to report to the Illusive Man, who assures him that despite the failures of his mission, he is still an asset to Cerberus.

Mass Effect: Deception
''This section features material from the first edition of Mass Effect: Deception, which BioWare has acknowledged contains discrepancies with other Mass Effect lore. Once revised editions of the book are released, this section will be updated.''

By the time of Mass Effect: Deception, Kai Leng's wounds have healed but he uses a cane when walking. He can still fight much as he used to, but the exertion can cause considerable pain in his legs. When a design for a DNA-specific bio-weapon tailored to attack the Illusive Man is stolen, Leng tracks it to an auction house in the city of Thondu on the batarian homeworld of Khar'shan. Leng steals the design and escapes. Later, Leng arrives on an uninhabited world in the Crescent Nebula and receives new orders from the Illusive Man: retrieve Paul Grayson's body from the Citadel and monitor the activities of David Anderson and Kahlee Sanders.

Mass Effect 3
Kai Leng is amongst the forces that Cerberus sends against Commander Shepard. Like Cerberus Phantoms, he is equipped with a palm device that projects a kinetic barrier, a projectile weapon in his right gauntlet, a tactical cloak and a sword for close-range combat.

Leng and a sizable contingent of Cerberus forces are deployed during Councilor Udina's attempted coup against the Citadel Council. He was close to assassinating the salarian councilor when Shepard and either Major Kirrahe or Thane Krios interferes. Leng either stabs Krios in a brief skirmish, or fires at the councilor only to hit a cloaked Kirrahe before escaping. If both Thane and the major previously died, or Thane was never spoken to before the coup attempt, Leng will successfully assassinate the councilor.

In a race to get to the remaining councilors, Leng disables Shepard's X3M, but ultimately fails his mission and is forced to retreat as C-Sec begins to regroup. As he escapes, Leng reports his failure to the Illusive Man and promises to never let Shepard get the better of him again. In the failed coup's aftermath it's revealed that Leng released a VI into the Citadel mainframe that erased all footage of himself. If the salarian Councilor was saved, Bailey presumes that Leng didn't believe Udina's plan would succeed.

Leng is later sent to the Temple of Athame on Thessia, where he kills a group of scientists waiting for Shepard. Leng remains hidden as the Commander discovers a hidden Prothean Beacon, awakening a Prothean VI named Vendetta, who holds information on the final Crucible piece known as the Catalyst. Leng then reveals himself, at which point Vendetta shuts down upon detecting that he is indoctrinated. Leng requests the Commander's attention and releases a small drone that projects a hologram of the Illusive Man.

The Spectre and the Illusive Man exchange words but remain unable to sway each other, so the latter orders Leng to take the VI. The Cerberus assassin then engages Shepard's team in combat but is unable gain a clear advantage, so he instructs his gunship to level the temple. The floor caves in, leaving Shepard alive but unable to act as Leng manhandles the Commander's squad, claims the data, and escapes.

After the mission, Leng sends a taunting message to Shepard titled "Evacuating Thessia", disguised as asari military command:

Samantha Traynor is able to track Leng to Horizon, where Henry Lawson is conducting experiments on refugees. At the same time, ex-Cerberus operative Miranda Lawson is there, looking for her sister. The Illusive Man reminds Leng to get the data but to kill Miranda only if she got in the way. Leng wounds Miranda when she confronts him, but otherwise leaves her alone. He manages to complete his primary objective and abandons the Lawsons to die, but is unaware that Miranda has tagged him so Shepard can strike back at Cerberus.

During the Alliance assault on Cronos Station, Shepard discovers video logs, detailing Leng's frustration with the Illusive Man's refusal to have the Commander killed. Eventually, the assassin reveals himself in the Illusive Man's office, interrupting the Commander's attempt to warn Admiral Hackett about the Catalyst being the Citadel. Leng and Shepard battle for the last time; the Commander's team versus him and groups of Assault Troopers, Phantoms, and Nemeses he periodically summons. Despite Leng's lethal skills and numerical superiority, he's unable to overwhelm Shepard. With his shielding depleted, he soon succumbs to attacks from Shepard's squad.

Despite his heavy wounds, Leng retrieves his blade and silently approaches Shepard, attempting a kill from behind. At the critical moment, Shepard detects him and counters his attack, causing him to gape in shock.

The Commander can either break Leng's sword while stabbing him with an omni-blade, or dodge the attack and stab him with the omni-blade, dedicating the kill to whoever died by Leng's hands during previous events: "That was for Thane and Miranda/Miranda/Thane/Kirrahe, you son of a bitch." If nobody mentioned was around, Shepard instead taunts him with "[n]o gunship this time, you son of a bitch." Whatever the outcome, Shepard ends the life of Cerberus' greatest assassin.

Trivia

 * According to The Art of Mass Effect 3, early concepts of Kai Leng gave him metal legs and hard armor, but this evolved into a stealthier appearance with a coat reminiscent of the one worn by Thane Krios. His face and body kept a few obvious cybernetic implants to imply that he had been modified since the events in the books to become even deadlier.
 * According to the Mass Effect novels, Kai has both Chinese and Russian/Slavic heritage, with the Chinese being the dominant of the two.
 * The weapon wielded by Leng appears to be based on a Japanese "ninjato"- a straight (and often shorter) variant of the samurai's katana.