L Lawliet (Japanese: エル・ローライト, Hepburn: Eru Rōraito), also known mononymously as L, Hideki Ryuga, and Ryuzaki, is the main antagonist of the manga series Death Note, created by Tsugumi Ohba and Takeshi Obata. He is an enigmatic, mysterious, and highly esteemed international consulting detective whose true identity and background is kept a secret. He communicates with law enforcement agencies only through his equally inexplicable handler/assistant, Watari, who serves as his official liaison with the authorities. Though his past is shrouded in mystery, he has gained a reputation as arguably the world's greatest detective.

Throughout the series, he observes and investigates the activities of the protagonist, Light Yagami, a high school genius. L attempts to expose and prosecute Light as the serial killer "Kira", who is responsible for killing criminals worldwide through supernatural means using a "Death Note". At the same time, he works to stop the killings and limit Kira’s actions, acting as a direct counterforce to him. As the series progresses, the psychological conflict between L and Light intensifies, as each attempts to uncover the other's identity through increasingly complex strategies. L serves as an ideological and visual foil to Light.

Tsugumi Ohba, the writer of the series, created L as a young adult, since he believed the story would not hold much interest if L were significantly older than his opponent, Light. For L's name, he wanted to use a single letter with a lot of significance; he considered "I" and "J", but eventually chose "L" after careful consideration. Ohba left most of L's character design to manga artist Takeshi Obata. Obata asked Ohba if L should be "unattractive". Afterwards Ohba included ideas in his thumbnails, including L's manner of sitting, "he's part English", and "he's listless". Ohba added details regarding L's mannerisms and his interests in sweets. Ohba credits Obata for the character designs. Obata commented that L's thumbnails by Ohba had no bags under his eyes, and that he had a "plain face with no expression" which was very useful. Obata drew L as an "attractive young man" until chapter 11, when the character appeared in person. After chapter 11, Obata and Ohba agreed to contrast his appearance with Light's.

During the development of the early manga chapters, Obata feared L would appear "so suspicious that Light would know instantly it was L if they ever met". When Obata's editor told him that he wanted L to have a face "looking cool based on the angle", Obata added black bags under L's eyes. Obata cited Devilman's Akira Fudou when stating that he believed that black bags were appealing. In addition, Obata thought of a "dead eyes" concept, which involved L having "all-black eyes" and "mostly no eyebrows". Obata believes that black eyes usually makes a character goofier, but the bags "sharpen the character's gaze". Obata believes that the design evokes "a feeling of mystery" and that the reader cannot determine L's true thoughts. Obata also said that the bags under L's eyes were useful for inspiring speculation about his lifestyle and background. The outfit Obata designed for L was a "simple" white, long-sleeved shirt and jeans, to convey that L does not put thought into choosing his clothing. In Death Note 13: How to Read, Ohba presented an initial rough draft of L and said that, with a "cool expression" and without the bags under his eyes, L looked like a different person.

Obata stated that the peculiar traits exhibited by L are best revealed "gradually". Obata added that if he drew L eating "mountains of sweets" before revealing his face, he would not have "much credibility as a super detective" and people would ask if he was "crazy". Both Ohba and Obata chose L as their favorite character from the series, with the former noting him as the "strongest" character in the series besides Light, and the latter due to "appearance, personality, everything". Obata said that he could never have created a character like L and that he enjoyed drawing him. Obata added that because of this, L was not "real" to him and that he liked that aspect of the character.

L's fighting style has been described as similar to capoeira. However, Obata has denied considering this when drawing L's fights, saying that he was thinking of the most effective way to kick someone whilst handcuffed. He added that if the style resembles capoeira, then this "adds another element to it" and "that makes me happy". When designing color illustrations, Obata assigned specific colors to the main characters to help "get the atmosphere right"; gold was assigned to L.

In the process of adapting L into the anime, several plot elements were added to flesh out L's human aspects. Kappei Yamaguchi, L's voice actor, specifically requested certain lines be added to emphasize L's vulnerable side, especially in regard to his relationship with his handler and father figure, Watari. L's rivalry and potential desire for a friendship with Light was also emphasized in episode 25, the final episode where L appears, in which L attempts to "stab Light in the heart" with a final conversation in the rain.

In the anime adaptation, he is voiced by Kappei Yamaguchi in Japanese, and by Alessandro Juliani in English. He is portrayed by Kenichi Matsuyama in the live-action film series, by Kento Yamazaki in the TV drama, and by Lakeith Stanfield in the American film.