Light Yagami is the protagonist of the series who acquires the Death Note and uses to to kill criminals to create a new world by writing their name in it while picturing their face, becoming known as the serial killer Kira. He views himself as a God after obtaining the Death Note.
He truly believes that by eliminating those he judges to be evil he can create a new world free of violence and crime where people can live in peace.
He represents what that a good person can fall into temptation. Light is a genius student, a good son, and caring brother yet he is consumed by the power of the Death Note and by the end of the series is unrecognizable from where he started.
"I will become the God of the new world"
-Light Yagami
L is a detective who has vowed to catch Kira and bring him to justice.
He is willing to risk is life for the sake of the investigation and the pursuit of justice
Light is constantly compared to L, in terms of intelligence and certain actions. And it is suggested that L is what kind of detective Light would have become had he not found the death note.
"This isn’t divine judgement, it’s the work of some childish killer who’s playing at divine retribution, that’s all"
-L
Ryuk is the former owner of the Death Note. The reason he dropped the Death Note into the human world is simple, he did it because he was bored.
He is an observer of the events of the series neither on Kira's side or L's
The user of a Death Note may make a deal with a shinigami at any time, training half of their remaining lifespan for the eyes of a shinigami allowing them to see any human's, who does not own a death note, name and lifespan above their heads. This in a sense is similar to making a deal with the devil
"Be warned any human who's used a death note can neither go to heaven nor hell for eternity"
-Ryuk
Misa Amane, also known as the second Kira, is an model and actor who came into possession of another Death Note that was dropped into the human world.
She witnessed her entire family being killed in a robbery, and endured a lengthy trial where the accused was likely going to walk- due to lack of evidence and rumours that he was being false accused.This caused her to slip into a deep depression.
However when Light became Kira he used the Death Note to kill the man who killed her family. Because of this she idolizes Kira and becomes a strong supporter and eventually one of his most loyal followers.
Sometime later she is assaulted by a stalker, however a shinigam watching her from the shinigami realm interferes. The Shinigami saves her life and leaves her his Death Note which she uses as the second Kira. Misa's power to kill surpasses even Light's as she made the deal for the shinigami eyes, allowing her the power to kill needing only a face (not a name and a face) at the cost of half of her remaining life span. After loosing her shinigami eyes she chose to make the deal for a second time, cutting her remaining lifespan in half once again, in order to continue serving Light this goes to show her devotion to him and his cause.
"Be careful what you do because God is watching your every move"
-Misa Amane
Soichiro Yagami is Light's father and chief of the Japanese police force.
He is the strongest willed character with a rigorous sense of duty.
Even when many other detectives quite the investigation, fearing for their lives, Soichiro Yagami chose to stay on the case. He claimed that he would never forgive himself if he sat by and watched evil triumph.
"Kira is evil, there’s no denying that. But lately I've been starting to think of it more like this. The real evil is the power to kill people. Someone who finds himself with that power is cursed. No matter how you use it, anything obtained by killing people can never bring true happiness"
-Soichiro Yagami
Touta Matsuda is a member of the Japanese task force working under L to catch Kira.
If Light represents evil, and L represents good then Matsuda represent the shade of grey in-between. Frequently throughout the series he gives his opinion that Kira is not all bad. He acknowledges that crime rates have decreased since Kira started killing and he admits to thinking that their are some people who deserve to die. However he also declares what Kira is doing is wrong, and that killing is wrong.
He is young, nieve, and idealistic. But he is also strong and determined. He is very human and can see both sides of the debate on whether Kira's actions are just but at the end of the day he is a police officer and will uphold the law.
"I’m not saying this to support Kira or condone the murders, but in the last few days throughout the world but especially in Japan we’ve seen observed a dramatic decrease in the amount of violent crimes committed"
-Touta Matsuda
Near (left) and Mello (right) are two of L's successors. While they share their mentors goal of capturing Kira they both have very different personalities.
Near like L works inside the law to collect evidenced arrest Kira. He is logical and never lets emotions get in the way of the case.
Mello joins the mafia willing to do whatever is necessary to achieve his goal, he is impulsive and driven by a desire to be the best detective.
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“Nobody can tell what is right and what is wrong, what is righteous and what is evil. Even if there is a god, and I had His teachings before me, I would think it through, and decide if that was right or wrong myself"
-Near
Mikami (left) and Takada are two of Kira's followers and are given pages of the Death Note to act as Kira on Lights behalf.
Completely devoted to Light and Kira like Misa they are extremes followers willing to do anything for what they believe in (unfortunately what they believe in is a serial killer with a god complex)
"There is no reason for me to question. God is absolute. My job is to do as God wishes."
-Teru Mikami