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, and white goggles with amber-tinted lenses. He wears black gloves that reach just below the elbow, as well as a pair of black boots and 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 helped him in the Kira case. Matt is very 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.
He 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. Matt 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. Matt 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 the 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 only seen again during Takada's kidnapping, where he distracts her bodyguards with a smoke grenade launcher, allowing Mello to kidnap her. When cornered, he tries to put up another smokescreen. Matt 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 wouldn't have revealed anything 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 Matt to die.
Later in the manga, a TV broadcast reports that his identity is unknown, and that the bodyguards were forced to shoot because he was showing a dangerous and aggressive behavior.
- 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.
- In the anime and manga, Matt is left handed.
- In the manga, Matt's car is a 1968 Chevrolet Camaro. RS/SS. While in the anime, it is a modified 1968 Plymouth Road Runner 383 with the tail light 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.
- Matt's true name, Mail, is pronounced as "Mile" and not "Mail."
- While Matt's official hair color is brown and his eye color is blue, fan art often depicts him with red hair and green eyes.
- 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.
- 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?"