D-Reaper

D-Reaper is a fictional character from the Digimon franchise. Although from the Digital World, the D-Reaper is not a Digimon. Instead, it is a computer program that "mutated" into an artificial life form. Exclusive to the Digimon Tamers series, the D-Reaper was a nigh unstoppable force existing only to destroy anything that went beyond its parameters, including humans and Digimon. The D-Reaper had no actual voice of its own, but it "used" Jeri Katou's voice to speak with.

Despite being a fictional character, the D-Reaper's backstory is linked with actual events and organisations, such as the outbreak of the Morris computer worm, one of the first computer worms to spread significantly and cause considerable damage, and ECHELON, an actual, highly secretive world-wide intelligence-gathering network.

Digimon Tamers
The program was created in 1970, as "the reaper" program created by the American Department of Defense to delete excess data and manage the growth of artificial intelligence. In this early form, it was visually similar to Pac-Man. The reaper’s first job was to delete the Morris worm virus. In the 80s, the reaper formed the basis for the security system of the Department of Defense's SIGINT system, ECHELON. In 1990, the D-Reaper attacked the fledgling Digital World, which had recently become populated by the Digimon. The Reaper went on to follow its program by deleting Digimon and absorbing their data and soon underwent an evolution of its own. It buried itself away beneath the Digital World and slumbered as it transformed into a sentient being.

By the time of the Tamers series, the newly created D-Reaper began to stir from the sheer amount of excess data that had been caused by Digivolving and the growth of the Digital World during its period of inactivity. It took Jeri to learn more about humans, creating its first Agent. The main part of D-Reaper followed the Tamers to the Real World through the Hypnos system and immediately began to spread over Shinjuku, keeping the Kernel Sphere high between the two towers of the Hypnos building, with Jeri sealed inside as its source of energy due to her grief. Only the Biomerged Digimon were able to fight it until it evolved into the Mother D-Reaper. Eventually, the D-Reaper began a global attack on Earth's electronic communication and most of the Digital World was destroyed by the D-Reaper. However, through the combined effort of everyone in Operation Doodlebug, the D-Reaper was regressed back into its original, harmless state.

Forms
The D-Reaper encountered by the Digimon Tamers was considerably different from the simple computer program it originated from. In the Digital World, the D-Reaper appeared in the form of a large, red chaotic mass of slime. Any data contacting the D-Reaper would immediately become absorbed and disappeared. Despite this, Digimon were able to fight the D-Reaper.

In the Real World, the D-Reaper still looked like a crimson mass. However, it could not absorb objects in the real world as quickly. It worked slower and adapted to the situation by studying the real world. Conventional weapons such as missiles appeared to have no effect on the D-Reaper. Using Jeri's negative energy, the D-Reaper of the Real World underwent an advance evolution, reabsorbing its agents and becoming the Mother D-Reaper. It managed to create more powerful versions of its most deadly agents and swallowed all of Shinjuku, Tokyo. The Tamers managed to get in (via the Red Card) and save Jeri before the Mother D-Reaper fell victim to the Operation. It was sucked into Juggernaut (Shaggai) and regressed back into a harmless program. Before she was destroyed, she looked like a large red mass with a strange, almost Aztec/Egyptian crown, and several eyes.
 * Mother D-Reaper (Episodes 49-51):

The combination of all the D-Reaper's agents at the Digital World surpassed its own boundaries and was to assimilate with Mother D-Reaper to complete the plan. However, it was dragged back into the Digital World by the Sovereigns, allowing the Operation to begin.
 * Cable Reaper (50-51):

Agents
To accomplish its goals in the real world, the D-Reaper utilized a variety of forms called "Agents". These agents were created from the main form of the D-Reaper. Most of these agents were connected to the main body through a red cord, except for the Jeri-type. When the cord was cut, the agents became weaker and easier to defeat.


 * Jeri-Type (40-51): This Agent was created for the purpose of espionage, posing as Jeri while the real one was in the Kernel Sphere. The Jeri-Type was unique among the Agents and was the only Agent that did not to need a cord to be linked to the D-Reaper. She eventually revealed her true form to Takato after manipulating the boy's feelings with her Mind Scan, tapping in key memories of Takato's relation to Jeri. She was driven off by MarineAngemon's Kahuna Wave attack. Initially the Jeri-type looked identical to the real Jeri, but when exposed it took on a more adult, blue-skinned, almost demonic form based on Jeri's form. She was eventually reabsorbed back into the D-Reaper when it became the Mother D-Reaper. An abnormally strong Agent, her face served as the Mother D-Reaper's first defense while the stronger, faceless version of herself became the last defense. She was finally destroyed by Gallantmon Crimson Mode.


 * Searcher (42-43, 45-46, 48): Created for information gathering, these small bird-like agents appear in large numbers. They are the only type of Agent not made for fighting. At first, the Tamers were wary of them, but they soon discovered they were relatively harmless. After the Tamers regained the ability to Bio-merge, Gallantmon was seen destroying many of these.


 * Pendulum Feet (42-43, 45): The first Agent of the D-Reaper the Tamers fought, it resembled a stereotypical wraith with a cloth-like body, a pumpkin-like face and cord-like limbs with sickles at the ends. It has the ability to mimic a Digimon's attacks. Built for aerial combat, it had a long-distance pendulum attack. After it was killed by Beelzemon Blast Mode. More appeared after the Tamers regained the ability to Bio-merge, but they were destroyed by Sakuyamon.


 * Bubbles (44-50): These are small squid-like agents built for ground assaults, these Agents have pulse cannons in their arms and move in groups.


 * Creep Hands (44-45, 50): This medium sized Agent was adapted for hand-to-hand combat. Its arms were extendable. Killed by Gallantmon and MegaGargomon in the first fight.


 * Horn Striker (46, 51): This Agent was a green beetle-like agent and an overwhelming opponent. When injured it could grow to gigantic proportions, roughly the same size as the enormous Mega Gargomon. It was very strong and took the combined powers of Sakuyamon, MegaGargomon, Justimon and Antylamon to kill it. They were mass-produced to serve as the second defense of the D-Reaper but were easily destroyed by Gallantmon Crimson Mode.


 * Paratice Head (47, 50): This multi-mouthed Agent was built for recon and battle. Its attack patterns were unpredictable, and its many mouths speak with Jeri's voice. Killed by Guardromon and Justimon. Another one was killed by Guardromon alone.


 * Optimizer (47, 50): This giant Agent was a carrier ship and carried Bubbles in its body. It could also fire a powerful blue energy blast from its mouth. Proved to be a difficult opponent for Gallantmon, Sakuyamon, Justimon, and Guardromon to defeat. It was destroyed by Gallantmon when he obtained Grani. A second Optimizer in the finale was destroyed by Sakuyamon's Amethyst Mandala attack.


 * D-Reaper Ball / Gate Keeper (48-49): This Agent was formed around the Kernel Sphere to protect it. It was assimilated back into the D-Reaper, forming the face of Mother D-Reaper in Episode 49.

Similar Concepts
The D-Reaper is in concept a hive mind, much like that of Star Trek's Borg or Homeworld: Cataclysm's The Beast. The Agents are not individual entities, but rather are part of a collective, a part of the D-Reaper controlled by a central mind. The D-Reaper also refers to itself as "the Collective".

There are also more similarities. When the D-Reaper absorbs and deletes Digimon, it absorbs its abilities. This is similar to the Borg's assimilation and the Beast absorbing people into itself. Interestingly, The D-Reaper also absorbs buildings, somewhat reminiscent of The Beast infecting ships and redesigning them, with bloodstain spots on the hulls.

Another concept of the D-Reaper is that of an ancient sleeping horror that reawakens and is ready to destroy the world. This is a theme in the works of H.P. Lovecraft, who Chiaki J. Konaka uses as inspiration in his works.