Kai Leng was created by Drew Karpyshwyn for the Mass Effect novels, and made his transition to the video-game medium in Mass Effect 3. His debut in the medium of comics was in Mass Effect: Foundation #2, written by Mac Walters.
The Retribution novel reveals that Kai Leng's heritage is predominantly Chinese, with some Russian/Slavic roots. In 2172, at the age of 16, he faked his credentials to enlist in the Alliance Military. He was assigned to a patrol and reconnaissance unit operating out of the volatile Terminus Systems, and quickly proved himself to be an exceptionally skilled and efficient soldier.
It was during this time that his hatred and disregard for alien life became evident; in 2173 he received an official reprimand for cutting off and collecting the badges of slain batarian pirates and mercenaries in the Exodus Cluster. His punishment was light, given his lack of priors and exemplary combat record.
4 years after joining the Alliance, he was selected for the elite N7 program at the Interplanetary Combatives Academy in Rio de Janeiro. After clearing the grueling regimen of tests and evaluations, he received the N7 designation and joined a restricted circle of military officers in the galaxy with the same privilege. His future seemed limitless, until the fateful day he attacked and murdered a krogan in a Citadel bar while on shore leave.
Following this, he was stripped of his N7 rank, dishonorably discharged, and sentenced to 20 years in prison for first-degree murder. The Illusive Man took note of Leng's potent combination of warrior's prowess and deep-seated xenophobia, and had a Cerberus squad break him out of the prison he was incarcerated in. Leng willingly joined Cerberus when offered, and served for nearly a decade as the Illusive Man's most discreet and ruthless wet-works operative. After Miranda Lawson defected from Cerberus in 2185, Kai Leng's status rose until he became the Illusive Man's right-hand.
Powers and Abilities
In addition to his skills as a soldier and assassin, Kai Leng received several cybernetic upgrades from Cerberus. These included mechanical legs to replace the ones that David Anderson blew away with a shotgun, and Phantom-class implants that granted him a degree of superhuman strength and speed.
Like all of Cerberus' Phantom-class operatives, he wields a monomolecular blade that can slice through practically any armor. He is also equipped with a laser palm cannon and a shield generator.