Matt - Death Note

Interesting facts
Matt is a great spy, as shown when he monitors Misa, Mogi, and Aizawa.
In Death Note 13: How to Use, it says that Matt likes American football.
Despite having brown hair, Matt is depicted in fan art as having red hair and green eyes. This is due to the absence of color in the manga, leading fans to speculate about his possible appearance.
In the anime and manga, Matt is ambidextrous, being depicted using his weapon with his left hand.
Matt is one of the few people in the series who participated in the Kira investigation and didn't die because of the Death Note.
Matt's real name, Mail, is pronounced "Mile".
Judging by Mello's apology (when he finds out that Matt died), it can be inferred that Matt and Mello were probably great brothers at Wammy's House.

Kira Case
In the Kira case, Mello asks Matt to monitor Misa, Mogi, and Aizawa. Later, at Mello's request, Matt decides to create a distraction so that Kiyomi Takada can be kidnapped.

Matt distracts everyone with a smoke bomb. Then, Matt escapes, pursued by Takada's agents. Thanks to this, Mello manages to kidnap her.

After a short chase, Matt is cornered by Takada's agents. Matt mentally wonders, "How many bodyguards does a girl need anyway?" He gets out of the car with his hands up, seemingly calm. The bodyguards point their guns at him, and he questions them, saying he's already been caught and confirming his involvement in the kidnapping. He then tells everyone that the bodyguards must have some questions, and that's why they won't shoot. Matt smiles confidently but starts taking several shots. Finally, he falls dead, and one of the bodyguards lowers his weapon, explaining that he was sure Matt wouldn't say anything; besides, death is the only way to pay for the crimes of being against Kira.

History
Matt lived at Wammy's House as a young teenager, and it is believed that Matt and Mello were close brothers while living in the orphanage. The exact time he arrived there is unknown. At some point in the story, Matt left the orphanage and began helping Mello with the Kira case.

Personality
Matt is very intelligent, known as the smartest person at Wammy's House and the third successor to L. He specializes in technology and is tasked by Mello with monitoring Misa Amane, Mogi, and Aizawa.

He has an incredible sense of humor, even asking, "Since when were the Japanese allowed to have such large weapons?", while at gunpoint. Matt is confident, and Death Note 13: How To Read mentions that his expertise in monitoring multiple computer screens simultaneously is what leads him to accomplish some unimaginable feats.

The manga also shows Matt's hideout filled with "healthy" food and a box of cereal. He is also frequently seen smoking cigarettes, even when bored. According to Death Note 13: How to Read, Matt enjoys video games and dislikes leaving the house.

Matt has brown hair and dark blue eyes. In the anime, he is seen wearing a red and black striped long-sleeved top, blue pants, black boots, and gray glasses with amber-orange lenses. He wears black gloves that reach just below his elbows and sometimes a cream-colored sleeveless vest with fur trim.

In the video game Death Note: Successor to L, Matt has blue-gray hair, but looks the same, although his eyes are never visible.

Matt (マット, Matto), is an investigator on the Kira case, acting as an accomplice to Mello.