Lelouch, also known by his alias Lelouch Lamperouge, is the central protagonist of the series. His birth name is Lelouch vi Britannia, and he is the eleventh prince of the Holy Britannian Empire, as well as the son of the 98th emperor, Charles zi Britannia, and his consort, Marianne vi Britannia. Following the assassination of his mother and the critical wounding of his younger sister, Nunnally, in an attack when he was ten years old, Lelouch confronted his father over the incident. This confrontation led to his banishment alongside Nunnally to Japan, where they were initially placed under the care of the Japanese prime minister and later became political hostages. When Britannia invaded Japan, Lelouch and Nunnally were discarded, and with the help of their mother's former allies, the Ashford family, they assumed new identities and were officially listed as deceased. Lelouch enrolled as a student at Ashford Academy, living a peaceful but cautious life while hiding his royal heritage.

Personality wise, Lelouch is exceptionally intelligent, calm, and highly strategic, often displaying a sophisticated and occasionally arrogant demeanor that stems from his aristocratic upbringing. At school, he presents himself as a friendly and laid-back student, but this persona is a mask. Underneath, he holds a deep resentment toward the Britannian nobility, whom he views as overprivileged and corrupt. His true nature emerges when he dons the identity of Zero, a masked revolutionary leader. As Zero, he is decisive, charismatic, and ruthless, able to inspire fierce loyalty while also manipulating others without hesitation. Despite his calculating and often cold exterior, Lelouch possesses a compassionate side, especially toward those he cares about, and he struggles with the moral weight of his actions. He is driven primarily by a desire for vengeance against his father and the empire that took his mother and exiled him, as well as by a deep, protective love for his sister Nunnally. His ultimate goal is to create a peaceful world where Nunnally can live without fear.

After receiving the power of Geass from a mysterious immortal woman named C.C., Lelouch gains the ability to issue an absolute command to any person he makes eye contact with, forcing them to obey once. This power, known as the Power of Absolute Obedience, has limitations: it works only once per person and requires verbal commands. Over time, Lelouch's Geass evolves and becomes more difficult to control, at one point activating involuntarily, which leads to tragic consequences when it forces his half-sister Euphemia to commit a massacre, an event that Lelouch is unable to prevent and which he later uses to rally opposition against Britannia. He eventually learns to suppress the Geass with specialized contact lenses. Beyond this supernatural ability, Lelouch is a masterful tactician and strategist, often thinking many steps ahead of his opponents. He is also a capable pilot of Knightmare Frames, notably the Gawain and later the Shinkirou, and he uses his intellect, charisma, and planning to build the resistance group known as the Black Knights from almost nothing.

His role in the story begins as a disaffected student who stumbles into a terrorist attack and is granted Geass. He uses this power to forge the identity of Zero, leading a revolution against Britannian rule in Japan, called Area 11. He builds the Black Knights into a formidable organization, gaining widespread support among the oppressed Japanese people. His actions escalate from guerrilla tactics to full-scale political and military confrontation, eventually putting him in direct conflict with his childhood friend and rival, Suzaku Kuruguri, who serves Britannia as a knight. A pivotal moment occurs when his Geass accidentally causes Euphemia to massacre civilians, an event that Lelouch unsuccessfully tries to stop by killing her, but which he then exploits to unite the resistance. Later, he uncovers the truth about his mother's death and his father's plans, confronting and ultimately defeating Emperor Charles. Lelouch then seizes the throne, becoming the 99th emperor of Britannia, and consolidates absolute power. However, his true aim is the Zero Requiem: a final plan in which he arranges for his own death at the hands of Suzaku, who is disguised as Zero, thereby uniting the world against a common enemy and allowing peace to emerge after his demise.

Key relationships in his life include his sister Nunnally, who is the emotional core of all his ambitions and for whom he is willing to sacrifice everything. With Suzaku Kururugi, Lelouch shares a deep childhood friendship that becomes a bitter ideological rivalry, as Suzaku believes in reform from within the system while Lelouch believes in rebellion and destruction of the old order. C.C. is his primary ally and the one who grants him Geass; their relationship evolves from a transactional pact into a bond of mutual understanding and reliance. Kallen Stadtfeld serves as one of his most loyal and skilled subordinates, and there is a strong, unspoken emotional connection between them. His half-siblings, including Clovis, Cornelia, Euphemia, and Schneizel, serve as antagonists or allies at various points, reflecting the fractured nature of the imperial family. Over the course of the story, Lelouch undergoes significant development: he starts as a vengeful prince, becomes a ruthless revolutionary, and ultimately embraces a messianic role where he willingly becomes the world's greatest villain in order to sacrifice himself for lasting peace. His abilities are not limited to Geass; his sharp intellect, strategic genius, and ability to inspire and manipulate are central to his success, and he frequently uses psychological warfare and long-term planning to outmaneuver his enemies.