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.

Kai Leng is voiced by Troy Baker.

Background
Leng's prowess in combat and xenophobic nature drew the attention of the Illusive Man, and Cerberus helped liberate Leng from prison. 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: 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 captured Grayson. During the mission Leng personally killed Liselle, the daughter of Aria T'Loak and Grayson's lover. He was 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 ordered Leng to exterminate Grayson when the experiment became too dangerous to continue, or if he got out of control. However, when a turian strike team raided the research facility that housed Grayson, Leng chose to rescue the Illusive Man rather than kill Grayson, meaning Grayson was rescued by the turians. After the assault, the Illusive Man sent Leng to Aria as Cerberus' representative, both to negotiate for her assistance in finding Grayson, and to keep an eye on her.

After Grayson escaped Omega, Kai Leng offered David Anderson and Kahlee Sanders - who were 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 was a Cerberus agent, Anderson and Kahlee attacked Leng, but he got the upper hand and asked again for their help, knowing Kahlee was the key to finding Grayson. They reluctantly accepted; however, when confronted with turian security guards near Leng's shuttle, they took their chance. After distracting Leng, Anderson tasered him, then convinced the guards to let him take Leng's limp body. Leng was then tied to the copilot chair with rope from the shuttle's med kit. During the journey, Kahlee realised the Reapers were sending Grayson to the Jon Grissom Academy, home of the Ascension Project.

Upon arrival at Grissom Academy, both Anderson and Sanders left 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 managed to free himself and get into the Academy. He later encountered a gifted biotic student named Nick, and needing Nick's biotics in lieu of a weapon, managed to persuade Nick that he was on his side.

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

Anderson refused to simply let Leng escape; however, Nick had been shot and was badly hurt. Anderson had to choose between saving Nick and letting Leng go, eventually choosing to help Nick - though not before wounding Leng in each leg to try and slow him down. Despite his injuries, Leng still managed to get back to the shuttle and escape. He was able to report to the Illusive Man, who assured him that despite the failures of his mission, he was 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, along with a sizable contingent of Cerberus forces, were 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 interfered. After a brief skirmish, Leng managed to escape after stabbing Krios/Kirrahe. If both Thane and the major had previously died, Leng will successfully assassinate the councilor.

In a race to get to the Council, Leng disabled Shepard's X3M, but ultimately failed his mission and was forced to retreat as C-Sec began to regroup. As he escaped, Leng reported his failure to the Illusive Man and promised to never let Shepard get the better of him again. It's revealed that Leng released a VI into the Citadel mainframe that erased all footage of himself. Bailey presumes that Leng didn't believe that Udina's plan would succeed.

Leng was later sent to the Temple of Athame on Thessia, while being invaded by the Reapers, where he killed a group of scientists waiting for Shepard. Leng remained hidden as the Commander discovered a hidden Prothean Beacon, awakening a Prothean VI named Vendetta, who held information on the final Crucible piece known as the Catalyst. Leng then showed him, at which Vendetta shut down upon detecting that he was indoctrinated. Leng requested the Commander's attention and released a small drone that projected a hologram of the Illusive Man. After the Commander and the Illusive Man exchange words, the latter ordered Leng to take the VI. The Cerberus assassin then engaged Shepard in combat but was unable to stop Shepard, so he instructs his gunship to level the temple. The floor caves in, leaving Shepard alive but unable to act as he claims the data. After the mission, Leng sent a taunting message to Shepard titled "Evacuating Thessia", disguised as asari military command:

Samantha Traynor was able to track Leng to Horizon, where Henry Lawson was conducting experiments on refugees. At the same time, ex-Cerberus operative Miranda Lawson was there, looking for her sister. The Illusive Man reminded Leng to get the data but to kill Miranda only if she got in the way. Leng wounded Miranda when she confronted him, but otherwise left her alone. He managed to complete his primary objective and abandoned the Lawsons to die, but was unaware that Miranda had tagged him so Shepard could strike back at Cerberus.

Shepard's final confrontation with Leng takes place during the Alliance raid on Cronos Station, when the assassin (along with a small squad consisting of seven Assault Troopers, two Phantoms, and a Nemesis) confronts the Commander on the observation deck of the station. Despite Leng's lethal skills, he's unable to overwhelm Shepard. With his shielding depleted, he soon succumbs to attacks from Shepard's squad.

However, despite his heavy wounds, Leng retrieves his blade and silently approaches Shepard to kill the Commander from behind. At the critical moment, Shepard detects him and counters his attack. 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. With either 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 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.