L is a very slim, tall young man with black hair and dark eyes. One of his most noticeable features is the shadow below each of his eyes, a result of sleep deprivation. L is always shown to be wearing blue jean pants and a long-sleeved, white shirt. He almost never wears shoes or socks, preferring to go barefoot while even in public.
L is quite secretive and only communicates with the world through his assistant, Watari. He never shows his face to the world in person, instead representing himself with a capital letter L drawn in "Old English MT" or "Cloister Black" typeface.
He goes by many different aliases in public, the most well known being "Ryuzaki". He requests that the Japanese Task Force calls him this soon after meeting them as an additional safety measure. The Task Force never learns his true name.
L is very intelligent, though his disheveled and languid appearance masks his great powers of deduction and many question his abilities upon viewing him. L tends to second-guess everything he is presented with, and is extremely meticulous and analytical. He is good at deceiving his opponents and is willing to take drastic measures to solve a case. Some of his tactics are quite bold, such as having death row inmate Lind L. Tailor pose as himself on live TV in order to draw out Kira, while others seem bizarre to those involved, such as handcuffing himself to suspected-Kira, Light Yagami. He is also shown to have a dry sense of humor, and isn't above making sarcastic remarks to people. Although he tends to be polite, to some (such as Task Force member Shuichi Aizawa), L can seem quite rude and uncaring at times.
Using subterfuge, misinformation, disinformation and an analytical knowledge of human nature to help lure a suspected murderer into a false sense of security and possibly make him carelessly over-confident, whenever L gives percentages to indicate how much he suspects a person of committing a crime, such as "five percent" he may in fact be over ninety percent convinced of their culpability. Although L tells Light that he is among the least likely suspects with one of the lowest percentages of probability, in reality L is "pretty certain" that Light is Kira. To quote series writer Tsugumi Ohba, "The truth is, he's a liar."
He has several quirks, such as preferring to crouch on a chair rather than sit, eating only sweet foods (like desserts, candies and fruits) and holding items by using only a thumb and a finger. He is often seen arranging objects and very intently stacking, or in other ways playing with, his staple food items. L is almost always encountered while performing actions that are considered inappropriate or rude in public. These actions/habits include biting fingernails, placing feet on furniture, slouching, chewing with an open mouth, talking with his mouth full, calling out personal observations that may offend others, etc.
Although he is often seen sitting and inactive, L retains a high athletic ability. L stayed in England for five years, and during that time he was the tennis champion in the England Junior Cup. He also has a knack for martial arts, which is demonstrated in his brief duel against Light. In episode 18 of the anime, Misa Amane tells him that "cake makes you fat", to which he replies that "you don't gain any weight as long as you burn calories by using your brain". He also says that if he sits normally, his reasoning ability would drop 40%.
HistoryL was found by Watari as a child and was taken to the Wammy's House orphanage. Sometime after, Watari realized that L had incredible knowledge and later assisted him in his cases. L became a detective at an unknown age and eventually gained a reputation as the greatest detective in the world, his opinion becoming highly valued. One of L's more famous cases before the Kira Case was the BB Murder Cases, detailed in the novel Death Note: Another Note. The killer, in this case, was Beyond Birthday, also known as BB or simply B, one of the four children chosen to replace L should he die, alongside A (deceased), Near (currently the new L) and Mello (deceased).
The first of many conflicts between Kira and L was when L placed a scapegoat, Lind L. Tailor, to determine which country Kira, as Light is known, is currently in, starting with Japan. Light kills Tailor, believing him to be L, only for the real L to cut the broadcast, replacing it with an image of his signature. Using a voice synthesizer, the L announces that Tailor was a decoy and a criminal on death row. He explains that Tailor's information was never made available to the public, so there was no way Kira could have killed him until now. L boldly taunts Kira, asking him to try to kill him, as Light stares at the TV angrily unamused. After several seconds, L learns that Kira needs the person's real name and face to kill the victim, otherwise Kira would have already killed him.
L announces that the video was aired only in the Kanto area of Japan as a ploy to determine the location of Kira. L, originally planning to air the video in other areas in Japan at different times, stated that it would not be necessary to continue broadcasting Tailor's footage. L says that he is now speaking directly to Kira and tells Kira that he will find him. As Light watches the broadcast, he also declares that he will find L and he will eliminate him.
Soon after, L took over the Japanese Task Force. Not long after this, because of the time of day during which the criminals die coincide with out-of-school hours, he deduces that Kira may well be a student. He tells those assisting him with the Kira case early on in the investigation that he suspects that Light Yagami is Kira, but can not obtain any concrete evidence. In several situations, Light seems to be proven innocent by the circumstances, but L remains skeptical. If Light were Kira, the case would be solved, and L has trouble letting go of this simple and complete solution. L can easily present his conclusions publicly at any time, and due to his reputation as the best mind in the crime-fighting business, his thoughts and words are always taken very seriously.
After his initial suspicions of Light, and in order to take his investigation to its next stage, L decided to join To-Oh University - the very same that Light himself attends - using the well-known name of a popular singer, Hideki Ryuuga. L attends To-Oh because he feels confident in his reasoning and interrogational skills and wishes to test his theory concerning Light's hidden identity by somehow confronting him, and perhaps provoking or tricking him to admit that he is indeed Kira. He intends to tell Light that he can "go on the offensive". L is well aware that this is something of a gamble, and knows full well that his act of direct confrontation could prove fatal, but as he's convinced he understands Light's thought process, he feels confident that the adversary will not yet risk revealing his secret identity by killing him.
When L introduces himself as Ryuuga, Light becomes alert and somewhat alarmed, but does not attempt to kill him - the name is conspicuously fake; however, Light has no way of knowing whether the person is the real L or a proxy acting under orders. He also reasons that L would have already introduced himself to Light's father earlier, and thus, were he to somehow kill L, this murder would instantly unmask him, proving that he is indeed Kira. If this person proved to be L's proxy, and his name really was Ryuuga, he might die, true, but L would live and know his identity, without ever having had to reveal himself to Light, so that L will have gained all the advantage. Also, while writing the name "Hideki Ryuuga" into the Death Note, the face of the pop singer bearing that name might enter Light's thoughts involuntarily, and that would cause the death of pop singer Ryuuga, which would also lead L to the obvious conclusion that Light is Kira. As such, L's expectations about the outcome of his daring opening gambit prove true, and Light finds himself in a stalemate situation, unable to act for the time being, as any attempt to rid himself of his hunters would result in confirmed suspicions, his subsequent and unavoidable unmasking, and, ultimately, his undoing.
Light has no other choice but to bide his time. When L is finally able to corner him, Light puts his master plan in practice. He temporarily gives up his Death Note to his Shinigami, Ryuk, erasing his memories about his time as Kira from his mind. Rem, Misa Amane's Shinigami, under instruction by Light to give it to someone who would use it selfishly, gives it to Kyosuke Higuchi of the Yotsuba Corporation. Now unaware of the fact that he was the original Kira, Light accepts L's offer to join the Task Force to hunt down Higuchi, known as the third Kira, although he is handcuffed to L throughout the entire case. Light proves very useful in helping to track down Higuichi, realizing the new Kira is connected to Yotsuba. When Higuchi is finally captured, Light touches his Death Note, thereby regaining his memory of when he was the original Kira. He then proceeds to killing Higuchi by using the Death Note paper he put in his watch before he lost his memories. Prior to L's death Light and L talk to each other for one last time on the roof of the investigation building.