Matthew Miltenberger was an expert scuba diver who was killed under mysterious circumstances, and then was briefly brought back to life by Ned. He is the first resurrected victim to be treated with a new personalized kindness, which Charlotte "Chuck" Charles brought to Ned's operation.
Little is known about the life of Matthew Miltenberger except that he was a professional scuba diver. He was found dead in the lobster tank of a franchise steak and lobster house under mysterious circumstances. According to the Narrator, Miltenberger was 37 years, six hours and 45 minutes old at the time of his death. It is likely that he was murdered, because a reward was offered for information surrounding his death, which private investigator Emerson Cod brought to the attention of Ned. 
Ned visited Miltenberger's body in the morgue and brought him back to life by touching him on the sternum. Ned planned to ask him about the circumstances of his death, as per a long-standing arrangement with Emerson in which the two solve the crime and split the reward money. But Chuck, recently resurrected by Ned, asked Miltenberger whether he had any last words, thoughts or requests. This was the first time the team had shown interest or compassion for the victim, and it inspired Ned to continue to operate in this fashion. 
It is unknown whether Ned, Chuck and Emerson determined what happened to Miltenberger or collected the reward money. 
Behind the scenes
Although the Narrator refers to the character as "Matthew," the credits list him as "Martin Miltenberger". 
Miltenberger's character was changed from the original screener version of the first episode. He was originally murdered in a public restroom, which was changed to being found dead in a lobster tank of a steak restaurant. He also was not identified with a specific occupation, although in the aired episode he is a professional scuba diver.