The main character of Death Note, Light is an extremely intelligent but bored 17-year old student. When he finds the Death Note, dropped in the human world by the shinigami Ryuk, he decides to use it to kill all criminals and earns the title Kira. His ultimate goal is to cleanse the world of evil to create a world without criminals and then reign over this new world as its "god."
L (Death Note)
The primary antagonist of the series, L is the world's top-rated detective and tasked with tracking down and arresting Kira. As such, he is Light's arch-enemy. He often takes drastic strategies to confuse and force the hand of his opponents, and his disheveled appearance disguises his brilliance. He enjoys sugar, and in nearly every scene including him, he is found eating cake or confectionery and drinking highly sweetened tea. His real name is L Lawliet.
A girl with an immense crush on Kira, Misa is a popular Japanese idol. She is immature and tends to refer to herself in the third person in an attempt to be cute. She is completely devoted to Light, saying that she loved him at first sight, although the feeling is hardly mutual- since Light merely views her as a rather annoying asset. In the manga version, she kills herself after Light's death, which is implied in the anime's finale. What happens to her after the film version is uncertain- the only remaining characters whose fates are revealed are L and the Yagami family- although she is still devastated when Light is killed.
Near (Death Note)
A calm and stoic character that appears in the second half of the series. In the anime and manga versions, Near is a primary candidate to become L's successor and calls himself N during the course of his investigations. He shares a number of similarities with L. Much like how L plays with things such as sugar cubes and forks, Near is frequently shown playing with toys or hair, and he is constantly shown sitting in an unusual manner. After L's death, he was asked to join forces with Mello, who refused (it is explained that Near lacks the emotional insight to beat L, while Mello is too emotional and impulsive). Near then gained the support of the Government of the United States and formed the Secret Provision for Kira (SPK). In the 'extra' manga story, set after the end of the series, Near states that, while he respects Light's drive for justice, he can never find his 'Kira' actions excusable. His real name is Nate River. :In the film L: Change the World L grants the name "Near" to a Thai boy who is a mathematical genius; L intends for Near to succeed him.
Mello (Death Note)
Mello, a character present in the anime and manga versions, was an orphan who grew up with Near and Matt in Wammy's House, Watari's shelter for "gifted" children. Like Near and Matt, Mello was one of the candidates to become L's successor. Similar to L's fondness for sweets, he is often seen eating bars of chocolate. Although Mello is quite intelligent, he often lets his emotions get the better of him. His goal in life is to surpass L and Near. His real name is Mihael Keehl.
Shinigami (Death Note)
Shinigami, or Death Gods, are demon-like beings who live in the Shinigami realm. Shinigami are functionally immortal, able to extend their lives indefinitely by writing the names of humans in their Death Notes. By writing the name of a human whose fated time of death has not yet come, Shinigami have their lifespan increased by the amount that human would have lived (e.g. a forty-year-old who would have lived to the age of sixty would yield twenty years). As Ryuk describes it, life in the Shinigami realm is incredibly dull; Shinigami do little more than gamble constantly, and using the Death Note is considered something workaholics do. The main Shinigami featured in the series are Ryuk, Rem and Sidoh. The only way to kill a shinigami is through love. (e.g. If a human had a set fate to die from a murder and a shinigami kills the murderer the shinigami will then turn to dust and evaporate. Just as Gelus and Rem did)