Detective L

L, who also uses the aliases Hideki Ryuga (流河 旱樹, Ryūga Hideki?), Ryuzaki (竜崎, Ryūzaki?), Eraldo Coil (エラルド＝コイル, Erarudo Koiru?), and Deneuve (ドヌーヴ, Donūvu?), the latter two for which he has developed reputations as the second- and third-best detectives in the world, is quite secretive and only communicates with the world through his assistant Watari. He never shows his face to the world, instead representing himself with a capital L in Cloister Black font. After meeting the Kira investigation team, he requests that the task force refer to him as Ryuzaki for discretion. The Kira investigation team never learns his true name. Ohba said that L is the smartest character in the manga because "the plot requires it."[12] Ohba also said that he personally views L as "slightly evil";[13] for instance, in chapter 109, Near discloses the fact that L claimed to pursue cases out of personal interest with no great sense of justice.

When asked about L's ethnicity, Ohba responded saying "I think of him as a quarter Japanese, a quarter English, a quarter Russian and... maybe a quarter French or Italian? Something like that."[3]

L's disheveled and languid appearance masks his great powers of deduction and insight. He tends to second-guess everything he is presented with, and is extremely meticulous and analytical. He has several quirks such as preferring to crouch rather than sit, eating only sweet foods like desserts and fruits, and holding items very delicately. L stayed in England for five years, and during that time he was the champion in tennis for the England Junior Cup. L also secretly assumes the identities of the world's second and third best detectives (Eraldo Coil and Deneuve respectively).

L suspects early in the investigation 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 with his reputation, is taken seriously.

Because of his initial suspicions of Light, L decides to join To-Oh University, the university that Light attends, using the name of Hideki Ryuga for investigative purposes. L attends To-Oh because he feels confidence in his reasoning skills and wishes to test them. He also intends to tell Light that he can "take the offensive." L understands that his act is dangerous and since he understands Light's thought process he feels confident that Light will not kill him at that point.[14]