Zero

Zero is a public masked identity, originally created and assumed by Lelouch vi Britannia. Although for a long time Lelouch remains the person behind the mask, throughout the conflict between Britannia and the Order of the Black Knights, Zero and his distinctive appearance remain a symbol of the anti-Britannian rebellion and the fight for an independent Japan.

Emergence
Lelouch made the original Zero costume by using his Geass on a craftsman to custom-make it for him and destroy the evidence. In this capacity, he first appeared to the future Black Knights in person, keeping his face and real name concealed. Zero then made his public debut during the operation to free the framed Suzaku Kururugi, revealing himself as Clovis la Britannia's killer.

Zero's fame quickly spread around the resistance groups throughout Japan. When Lelouch announced The Order of the Black Knights to the world, he remained its undisputed leader as Zero until the Black Rebellion, with C.C. sometimes donning the costume to act as a decoy for him. Zero became a symbol in Japan, a messianic figure, especially after Euphemia li Britannia was accidentally turned by Lelouch's Geass into an enemy of the Japanese and ordered their massacre.

During the first assault on Tokyo, however, Lelouch left the Black Knights behind to seek his kidnapped sister, Nunnally vi Britannia. In his absence, the Black Rebellion crumbled, and Britannia declared Zero dead.

Return
After C.C. restored Lelouch's memories, previously meddled by Emperor Charles zi Britannia when he was captured by Suzaku, Lelouch once again assumed the identity of Zero, announcing his return to the world and freeing and reforming the Order of the Black Knights. For a long time, many higher-ups in Area 11 did not believe him to be the same Zero who led the Black Rebellion, including Suzaku, who knew Lelouch was the previous Zero but believed he still did not have his memories returned.

For a brief time during Lelouch's depression over Nunnally vi Britannia's plans to recreate the Special Administrative Zone of Japan, Kallen Kozuki considered taking over as Zero, with C.C. remarking how metaphorically heavy the mask was. Lelouch finally returned to his role and came up with a new plan to move some of the Japanese out of Britannian control. Per this plan, Zero negotiated his exile from Britannia in exchange for assembling one million people to participate in the Special Administrative Zone. However, what he actually did was distribute one million Zero costumes among the participants, thus making them all fall under the provision. These "Zeros" were evacuated to Penglai Island, which became the new headquarters of the Black Knights, having assumed the function of the United States of Japan's government-in-exile.

Some time prior to the creation of the United Federation of Nations, Zero became the official CEO of the Order of the Black Knights. However, after the Second Assault on the Tokyo Settlement, Schneizel el Britannia revealed the truth about Zero's real identity and his use of Geass to the Black Knights, causing them to turn on him. Lelouch fled from the Black Knights and Schneizel, rescued by his "brother" Rolo Lamperouge, and abandoned the Zero mask, acting publicly as Emperor Lelouch vi Britannia upon his ascension to the throne one month later. The Black Knights officially hid the truth about Zero's identity and escape, declaring him dead from his injuries in the battle.

Passing of the torch
In three months after Lelouch established himself as Emperor of Britannia, he built up a public image of a tyrannical enemy of the world. It was then that Suzaku Kururugi appeared in the Zero costume and assassinated Lelouch, thus fulfilling their plan for Zero Requiem. Per Lelouch's wish, Suzaku &mdash; officially believed killed in the assault on Damocles &mdash; continued his life as Zero, now considered savior of the world, unable to show his face. As the second Zero, Suzaku remained at Nunnally's side; and Schneizel, previously forced into serving Zero by Lelouch's Geass, turned his loyalty to the new Zero after the Emperor's death.

Policies
Zero (Lelouch) seems to follow the belief of "the ends justifying the means", and is willing to commit evil, to destroy another evil. He doesn't appear to care who knows it, as he publicly declares that belief. Zero is shown to have little concern for innocent lives, as when he mentions to Kallen about how innocent lives would have to be sacrificed. In the end, Zero states his primary goal is achieving his own concept of justice, and in so, is willing to do anything to achieve that justice. While he seems to care little for Britannian lives, but does not discriminate during attacks, as he orders the Black Knights to not harm the Ashford Academy students. Zero, at first glance, seems to have little concern for the lives of his subordinates, save perhaps for the stronger ones. However, this is presumably a ruse.

Costume design
The Zero costume consists of a tight dark purple suit (changed to a light purple in R2) with golden stripes and long, wrapped sleeves. The outfit combines Victorian fashion with that of a sleek bodysuit, elegant but practical; worn over it is a black and gold cloak with crimson spandex inside and an enormous black cape encircling the head. Its immediately recognizable feature is a spiky black and indigo mask with a long variation of the Geass sigil stretched over its bottom, completely hiding the wearer's face &mdash; appearing opaque from the outside, but transparent from the inside. By unknown means, a small part of the mask can be signaled to slide down, exposing the wearer's left eye; this feature was designed by Lelouch to let him use his Geass without revealing his face.

Quotes (as Lelouch)

 * "People of Japan and all who are oppressed by the empire of Britannia, long have I waited, all through the struggles against Britannia's injustices, I waited for them to come to their senses, but that hope was betrayed, by an act of barbarism that can only be called genocide. ... Euphemia is the symbol of Britannia's hypocrisy, a murderer cloaked in the flag of a nation. ... I hereby declare our independence from Britannia, but don't take this to mean the resurrection of your fallen nation, we will not turn back the hands of time! The new Japan we go on to build, shall be one broad enough to accept all peoples, histories, and ideologies. Where the strong shall not reign over the weak, and it shall be called The United States of Japan!"
 * "Yes, I am Zero, the man who leads the Black Knights, who challenges the Holy Britannian Empire; The one who holds the entire world in his hand."
 * "People! Fear us, or rally behind us as you see fit. We are the Black Knights. We of the Black Knights stand with all those who have no weapons to wield, regardless of whether they be Elevens, or Britannians. The Japan Liberation Front cowardly took innocent Britannian civilians hostage, and then mercilessly executed them. It was a wanton and meaningless act, therefore they have been punished, just as former Viceroy Clovis was punished for ordering the slaughter of countless unarmed Elevens. We cannot standby and allow such cruelty to be carried out, and so we made him pay for his actions. I will not repudiate battle on a fair and level field, but neither will I tolerate a one-sided massacre of the weak by the strong. The only ones who should kill are those who are prepared to be killed! Wherever oppressors use their power to attack those who are powerless, we shall appear again, no matter how mighty, how formidable our foe may be. Those of you in power, fear us! Those of you without it, rally behind us! We, the Black Knights, shall be the ones who stand in judgement of this world!"
 * "I am Zero! People of Japan, I have returned! Hear me Britannia! All you who have power, heed my words carefully. I am burdened by sorrow. War and discrimination... Malicious deeds carried out by the strong... The same abhorrent interplay of tragedy and comedy... The world has not changed. The people still suffer. That is why the resurrection of Zero was necessary. So long as the strong oppress the weak, my rebellion will continue to grow. It begins today with the divine punishment I have wrought upon the inept and foolish Viceroy Calares. I shall fight against all those who abuse their power. Therefore once again, here and now, I declare the establishment of the United States of Japan! Starting from this moment, this room shall be the first dominion of the USJ! Race, ideology, and religion will not matter. Being a citizen will have but one requirement: to do that which is just!"
 * "What do you do when there is an evil you cannot defeat by just means? Do you stain your hands with evil to destroy evil, or do you remain steadfastly just and righteous even if it means surrendering to evil?"