Lelouch vi Britannia (Japanese: ルルーシュ・ヴィ・ブリタニア, Hepburn: Rurūshu vi Buritania), whose alias is Lelouch Lamperouge (ルルーシュ・ランペルージ, Rurūshu Ranperūji), is the main protagonist of the Sunrise anime series Code Geass: Lelouch of the Rebellion. In the series, Lelouch is a former prince from the superpower Britannia who is given the power of the "Geass" by a witch known as C.C. Using the Geass and his genius-level intellect, Lelouch becomes the leader of the resistance movement known as "The Black Knights" under his alter ego Zero (ゼロ) to destroy the Holy Britannian Empire, an imperial monarchy that has been conquering various countries under the control of his father.

Besides Code Geass, Lelouch has appeared in multiple related adaptations; in Nightmare of Nunnally, the protagonist has become a superpowered human combined with C.C.; in Akito the Exiled, he is a strategist brainwashed by his father as a supporting character; and in Code Geass: Lelouch of the Re;surrection (2019), he is leading his forces in an alternate sequel to the original television series. He is also present in video games based on the series as well as crossovers such as Super Robot Wars, which depict alternate scenarios for his role in the Code Geass series while still piloting his mecha, the Shinkirō.

Inspired by the tokusatsu series Kamen Rider, the director Gorō Taniguchi created Lelouch with the idea of having an evil protagonist who would appeal to the audience. Lelouch was designed by a group of manga artists called Clamp, who aimed to create a stylish and visually appealing character. Taniguchi handled the character alongside writer Ichirō Ōkouchi. Ōkouchi and Taniguchi agreed on the film Code Geass: Lelouch of the Re;surrection as his final appearance in the franchise. He is voiced by Jun Fukuyama, and his younger self is voiced by Sayaka Ohara. In the English dub, he is voiced by Johnny Yong Bosch, and his younger self is voiced by Michelle Ruff.

Lelouch has been recognized as one of Japan's most popular characters during the time Code Geass aired, appearing at the top of several polls. Publications for anime and manga saw Lelouch as an interesting character, and his character arc brings major depth, especially when being compared with his rival and friend Suzaku Kururugi. His voice actors, Fukuyama and Bosch, have been praised for their work as Lelouch's voice.

The basic idea for the plot of Code Geass consisted of a "hero" who led a secret organization, which later developed into a conflict between two characters with different values and who belonged to the same military unit, who eventually became Lelouch and his best friend Suzaku Kururugi. According to writer Ichirō Ōkouchi, he did not want the story to revolve around Lelouch and Suzaku's points of view. Neither are they mouthpieces for his own personal ideologies. The prototype of Lelouch is Rokuro Makube, the antagonist in Osamu Tezuka's manga The Vampires. Director Gorō Taniguchi wanted Lelouch's actions in the television series to have a major impact on the cast, later resulting in the creation of the movie to explore it further. Writer Ichirō Ōkouchi says that while Lelouch is important to bring peace to the world at the cost of his life, Suzaku and several other characters have to remain alive to live up to his legacy. That end is to Lelouch and to Suzaku both the punishment and the salvation at the same time. Suzaku killing Lelouch was decided by the staff ever since the series began.

Despite similarities between Lelouch and Char Aznable from Mobile Suit Gundam, Taniguchi claimed he was more inspired by the TV series Kamen Rider in creating Lelouch and asked Ōkouchi to avoid Gundam-like characterizations. Just like Lelouch, the boss of Shocker begins by creating an evil organization, but by sheer bad luck, his childhood friend becomes Kamen Rider and comes to destroy him. Regardless of his strategies, he is always defeated by Kamen Rider. Nevertheless, the director ended up realizing that both Lelouch and Suzaku were too similar to Char and Gundam protagonist Amuro Ray, respectively, citing Lelouch's mask and Suzaku piloting a white mecha. Taniguchi found Lelouch and Suzaku's relationship was different from the Gundam leads, as in the case of their backstories, the two did not meet on the battlefield but instead in their childhood, similar to a holiday when Lelouch and Nunnally were taken to Suzaku's house.

While designing the concept art for Lelouch, the series original character designers, Clamp, initially conceived of his hair color as being white. Nanase Ohkawa, head writer at Clamp, said she had visualized him as being a character to which everyone could relate as being "cool", literally, a "beauty". While developing the character during the initial planning stages, the series' core staff at Sunrise, director Gorō Taniguchi, Ōkouchi, and the production team discussed numerous possible influences for the character with Clamp, such as the Japanese idol duos KinKi Kids and Tackey & Tsubasa. When designing the character, Taniguchi asked Clamp to give him a strong aura. He originally did not want Lelouch to open up to his friends, which is why he shows a coldhearted personality when first seen, most notably when interacting with his high school friends. Taniguchi asked designers Takahiro Kimura, Yuriko Chiba, and Kazuya Murata for help when animating the character, most notably whenever Lelouch moves his hands and does poses while talking. In the making of the film trilogy, Taniguchi was asked to change events in the relationship Lelouch and C.C. have.

During the early planning stages for Lelouch's alter ego, "Zero", Clamp wanted to create a mask never witnessed prior in any Sunrise series. Zero was one of the earliest-developed characters. Ōkouchi wanted a mask to be included as a part of the series because he felt that a mask was necessary for it to be a Sunrise show. In the early designs of the character, Zero possessed long silver nails. Tanaguchi claimed that Lelouch's original view in the eyes of the fans changed from his anime persona to more like the manga one. The staff thus wanted Lelouch's characterization to be more realistic. In 2019, during the promotion of the upcoming movie, Taniguchi said that he wanted to leave Lelouch's death ambiguous, but later rescinded that statement by explaining that the TV series was not written with the idea of Lelouch being alive in mind. For the original video animation Code Geass: Akito the Exiled, director Kazuki Akane told the artists in charge to dress the imprisoned Lelouch and Suzaku in just their underwear so they would not be able to hide their weapons, but as it was too pathetic, he told the staff that they were going to have to wear only their underwear. Though Lelouch remains inactive in the finale, Akane wanted his last scenes with Suzaku to feel meaningful.