L is the pseudonym for the impossibly brilliant detective-for-hire from the manga/anime Death Note.
As a nameless, faceless sleuth L had, previous to the unfolding story in Death Note, helped the authorities worldwide on otherwise unsolvable cases. Not much is known about him except he possesses incredible intelligence and deductive skills. He communicates with the police agencies through a laptop displaying a white screen and an "L" and a microphone. However after beginning the Kira case, it becomes clear to him that he cannot solve the murders, by a person who can seemingly "will" a victim to die, without revealing himself.
Without spoiling any of Death Note's amazing story, L is an orphan whose deductive abilities have been encouraged to the point where now, in his mid-twenties, he is very insightful; earning him the label "Number One Detective in the World" — a modern-day Sherlock Holmes.
He has quite an eccentric way about him, sitting on chairs with his knees tucked up to his chest, dangling items gingerly only using his thumb and forefinger, and hardly ever looking anybody in the eye when speaking to them. Also, he seems to have a distinct penchant for sweets.
Going by the name Ryuzaki (also an alias) he helps the Japanese police force track down the mysterious Kira.
Other aliases used: Eraldo Coil, Deneuve.