Kai Leng is an assassin working for the Axis Joint Military. Leng was formerly a lieutenant and N7 marine in the Alliance of Nations known for having anti-alien attitudes. He is described as being Riz'ro Earth-born with features that show his dominant Chinese heritage. His allied rival was Raiden.
While little is known about Kai Leng's early life, Alliance records show that he enlisted in the Alliance Military on November 14, 1452 N.E 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.