Nebula

The Nebula Corporation (commonly mistranslated as Nebra) is a large and powerful organization that is mentioned several times in not just Durarara!! but in Ryohgo Narita's other novel series Baccano and Etsusa Bridge. They play rather small, but still very influential, roles throughout each series and serve as one of the many small ties that connect most of Narita's novels together.

Public Face
At the time Durarara!! begins, Nebula functions primarily as a pharmaceutical company whose main office is located in the U.S. It is unknown if they have always used a Pharmaceutical company as a public facade however they have been shown to have influence in politics as well as ties to certain mafia families. In the first half of the anime, Nebula is attempting to buy out Yagiri Pharmaceuticals in an attempt to further expand their business in Japan. This was later proven to be a cover up for their true goal, obtaining Celty's head which was in Namie's possession at the time. Although they succeeded in buying out Yagiri Pharmaceuticals, Namie had already fled along with the head and dropped off the radar, eventually seeking refuge with Izaya without their notice.

True Intentions
Due to it's presence in Baccano, it can be safely assumed that Nebula has been active at least since the early 1900s. Aside from their various public personas, Nebula's true trade is studying and experimenting with supernatural beings and creatures of myth such as the case with Celty, the dullahan, and Ruri Hijiribe. Their ultimate goal appears to be obtaining the secret to Eternal life although it is not entirely clear what they intend to do with such information. In all three of the above mentioned series, Nebula has had some kind of indirect influence on many of the major events that transpire.

Notable Employees and Associates
Senator Manfred Beriam (1930's): A powerful politician searching for immortality to abolish it.

Renee Paramedes Branvillier (1930's): is an immortal researcher using the company to advance her experiments. She ultimately becomes its leader in certain story lines, implied to still lead Nebula to the present Durarara story line.

Godfather Placido Russo (1930's): The leader of the Russo Crime family, Renee uses them as a means to quell a series of violent acts to their organizational buildings in Chicago by giving the don incomplete immortality. When they fail, they disassociate from the Russo and Placido is consumed by Renee.

Godfather Bartolo Runorata (1930's): The leader of the Runorata Crime family and appears to be more interested in immortality for the science as opposed to the secret of immortality itself.

Shingen Kishitani : One of their chief scientists when the supernatural is involved. Frequently disregards Nebula's goals in favor of his own frivolous endeavors. Is only affiliated with them for the research funding.

Emilia Kishitani : Shingen's wife and assistant. Share's her husbands interest for the supernatural and the unusual.

Egor (hired mercenary): Hired by Shingen to capture Ruri Hijiribe until she was ultimately rejected for testing.

Nebula Employees (1930s): Their very own employees, 1200 of the staff of Mist Wall in New York were unwillingly granted immortality via vaccine inoculations and were revealed to have been done so during an orchestrated incident to test the limits of incomplete immortality. It is unknown what became of most of the staff after the incident. It is also unknown if the present story line employees of Durarara and Etsusa Bridge are granted incomplete immortality discreetly.

Notable Test Subjects or Candidates for Testing
Celty Sturluson : Agreed to testing in exchange for safe passage to Japan. Company has since lost interest in Celty's body and is more focused on finding the head.

Ruri Hijiribe : Considered for testing by Shingen but was ultimately rejected by his superiors due to the belief that she would yield very little new discoveries.

Shizuo Heiwajima : Considered but ultimately rejected as a viable test subject (most likely due to his volatile temper).

Huey LaForet (1930s): One of the Original Immortals. Prisoner held in Alcatraz during the 1930s for an unknown period of time.