Matt (マット, Matto) is Mello's friend who lends him aid on the Kira case. Like Mello and Near, and earlier, L, Matt was raised at Wammy's House—Watari's orphanage for gifted children in Winchester, England.
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, brown boots, and white goggles with amber-tinted lenses. He wears black gloves that reach just below the elbow and at times, a cream-colored, sleeveless vest with fur trim.
In the video game Death Note: Successor to L, Matt has blue-gray hair but otherwise looks the same, though his eyes are never visible.
Matt is Mello's assistant and longtime friend who helps him with the Kira case. He is highly intelligent, known as the third smartest child at Wammy's House and the third successor to L. His specialty is technology, and he is tasked by Mello to monitor the activities of Misa, Mogi and Aizawa.
Matt is shown to have a dry sense of humor, asking, "Since when were the Japanese allowed to have such big guns?" while standing at gunpoint. He is confident, and his cockiness while monitoring multiple computer screens at once is what leads him to make a few mistakes.
In the manga, Matt's hideout is shown to be littered with junk food and a box of cereal. Matt smokes cigarettes and is seen doing so even while driving. He enjoys and is often seen playing video games, and he dislikes going outside. Takeshi Obata described Matt's concept as a "young man who loves gaming and doesn't really care much about the world."
Matt is first seen in the manga as Mello's accomplice in spying on Misa Amane  and later, Mogi and Aizawa. Matt follows Misa and observes her shopping with Mogi, then calls Mello with his cell phone. Matt describes Misa as "cute"  and states that her age appears to be anywhere from fourteen to twenty years old. Later on, Matt calls Mello again, having been watching Mogi and Aizawa via camera. He informs Mello that the two have come out of a building and are having what appears to be a serious conversation. Matt makes another phone call to Mello after having let his guard down and losing track of Misa and Mogi, who used a delivery truck as a disguise to sneak out of the building. Matt then follows Mello to Japan in their pursuit.
He is seen again during Takada's kidnapping, where he distracts her bodyguards with a smoke grenade, allowing Mello to abduct her. When cornered, Matt tries to put up another smokescreen. He calmly surrenders but is shot multiple times. After the cease-fire, when Matt falls to the ground, the bodyguards state that they never intended on bringing him in alive because of their belief and loyalty to Kira, claiming that Matt would have revealed nothing about the kidnapping and asserting that "Death is the only way to pay for crimes against Kira." While driving the truck in which he is holding Takada hostage, Mello sees the news of Matt's death broadcast on TV and apologizes, having never intended for him to die.
Later, a TV broadcast by NHN's News7 reports that his identity is unknown and that Takada's bodyguards were forced to shoot because he was showing dangerous and aggressive behavior.
- Matt's true name, Mail, is pronounced as "Mile" and not "Mail."
- Matt appears briefly in the Death Note One-Shot Special during Near's flashback. He is seen at Wammy's House listening to L talk to the children.
- Matt is possibly left handed, judging from how he reaches for his gun with his left hand.
- In the manga, his car is a 1968 Chevrolet Camaro RS/SS, while in the anime, it is a modified 1968 Plymouth Road Runner 383 with the taillight panel from a 1969 Dodge Coronet 440. Others argue that the car is a 1970 Chevrolet Chevelle SS 454, but there is no significant proof of either.
- While Matt's official hair color is brown and his eye color is blue, fan art almost always depicts him with red hair and green eyes. This is because he became rapidly popular with the fandom as soon as he debuted in the manga, so a color scheme for him was already unofficially agreed upon by the fans long before his official hair and eye color were revealed in the anime.
- While the letter Matt uses to identify himself is never really shown, fan art often depicts his letter as being a lowercase m to differentiate from Mello's uppercase M, which also doesn't appear in canon.
- While Matt is shown multiple times in the manga, due to the way the anime differentiates between focus and narrative, the only scene depicting him in the anime is when he distracts the Kira guards in order for Mello to kidnap Takada. This prevents fans who haven't read the manga from properly connecting with and understanding him, dubbing him "The Coolest 5 Minutes of the Anime."
- “Bored out of my mind!”
- (To Mello) “Anyway, it's too boring to keep watching something that has no movement.”
- (To Mello, about Misa) “Then why don't we swap our jobs? Yours would be better, since you can listen secretly to a cute girl.”
- “Since when were the Japanese allowed to carry around such big guns?”
- “How many bodyguards does one damn woman need anyway?”
- ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 From Death Note 13: How to Read, page 27.
- ↑ This is an accurate conversion of Matt's height. Viz's official English release incorrectly converts his height to 5' 5" instead. See Death Note 13: How to Read for more information.
- ↑ Death Note 13: How to Read [need page number]
- ↑ Death Note 13: How to Read, page 136
- ↑ Chapter 83, page 10
- ↑ Chapter 85, page 4
- ↑ Chapter 85, page 8
- ↑ Chapter 87, page 8
- ↑ Chapter 98, pages 17-21
- ↑ Chapter 99, Pages 1-3
- ↑ Chapter 99, page 9