Calumon is a supporting character in Digimon Tamers, and serves as the incarnation of the process of Digivolution itself. The Calumon of Digimon Tamers also appears in several movies, manga, and video games set within the Digimon Tamers continuity.
Calumon is a small, cute white creature with large eyes and comparatively small limbs. His ears, usually short, can extend, usually when Calumon is happy or excited, and he can even use them to fly. His forehead bears the Zero Unit, which can manifest as the gem-like "Crystal Matrix".
Calumon is the "Catalyst", the physical incarnation of the "Digi-entelecheia", otherwise known as the "Light of Digivolution". Calumon's power sometimes manifests as random digivolving in nearby Digimon when he is excited, but can also be purposefully channeled through the Crystal Matrix whenever the Tamers use a Digivolution or Blue Card.
Calumon is, above all else, innocent, optimistic, and unfailingly cheerful. Despite Impmon's constant bullying during their time on Earth, Calumon never shows the demon any illwill, and even after being kidnapped by Makuramon, Calumon quickly cheers up and begins playing with DigiGnomes once he escapes. Calumon is decidedly more childlike in the English and Brazilian dubs of Tamers, as opposed to the Japanese and German versions. In the Japanese and Brazilian versions, Calumon has a verbal tic of adding "-culu" at the end of its sentences, or "-calu" in the Southeast-Asian English dub. The American dub also gives him an appetite for cream puffs.
Although Calumon lacks a Tamer, he is quite friendly with the Tamers, and has particularly close bonds with Rika and Jeri. Although Rika initially responds with disdain for the little ball of fluff, his cuteness and indomitable cheerfulness eventually break through even her hard exterior, and he is one of the few people she shows any affection toward. When Jeri is taken by the D-Reaper, Calumon is the one to sense her location, and when he and Beelzemon Blast Mode are captured as well, Calumon tries continuously to lift Jeri's spirits and get her through her depression. Calumon continues to stay close to Jeri, even staying with her throughout Parasimon's attack on Tokyo.
- Shining Digivolution: Allows every Digimon in the Digital World to reach its full potential by digivolving to Mega.
By the 2000s, the computer network had expanded exponentially, creating a huge influx of data into the Digital World, which the Digimon used to "digivolve" and change. Though the system was large enough to handle this load, the Sovereign Azulongmon sensed that it could reawaken the D-Reaper, and with the help of the DigiGnomes he transformed the "Catalyst" program into the form of a Digimon, Calumon. Though this greatly slowed the growth and Digivolution of Digimon, it was not enough to stave off the D-Reaper, which soon reactivated. At the time, though, it was still in an extremely primitive state, and the Sovereigns attempted to find solutions before the problem became too huge. Azulongmon eventually decided to let Calumon loose in the Real World.
Calumon initially sees the events in the Real World as a fun game, and thinks of the humans as simply another species of Digimon.
When the Tamers manage to get embroiled in Mephistomon's scheme, Calumon tags along and is responsible for causing Growlmon, Gargomon, and Kyubimon digivolve to Ultimate when he gets scared by Gulfmon. 
After Rika rescues Calumon from the Chaos, the Sovereigns assemble and inform Calumon of the truth. They exhort him as the Catalyst to once again release his light to create a massive army of Mega-level Digimon, in order to defeat the D-Reaper. With the energy granted him when the DigiGnomes sacrifice themselves en masse, Calumon is able to become the Digi-entelechy once again, and empowers the Digimon across the Digital World with his "Shining Digivolution". In thanks, the Sovereigns grant Calumon's only request, to continue to live among his friends as a Digimon.
In the city, Calumon suddenly senses Jeri's presence within the D-Reaper mass, and begins heading toward its center. He crosses paths with Impmon, who stops him from blindly rushing into the chaos and decides to assist, filled with remorse for what he had done to Jeri and Leomon. With Impmon carrying him in the form of Beelzemon Blast Mode, Calumon locates the invisible Kernel Sphere where Jeri is being held and manages to get in through a hole made by Beelzemon, but as soon as he gets in, Beelzemon is captured and bound by the now-visible Kernel's tentacles. Trapped, Calumon makes repeated attempts to raise Jeri's spirits, without success, but his shouting eventually rouses Beelzemon, who is ejected from the sphere due to his role in Jeri's memories. When Jeri makes a weak attempt to strangle herself with her puppet, Calumon's frightened words finally reach her and snap her out of her stupor, and she begins to fight back against the D-Reaper's manipulations. As the D-Reaper is slain through the combined efforts of the Tamers and Operation: Doodlebug, Calumon shields Jeri in a bubble of positive energy and the pair escape towards the others; as the D-Reaper mass is dragged through the wormhole, the reunited group leaves the D-Reaper Zone together. However, the side effects of the Juggernaut make it impossible for the Digimon to remain in the Real World, and after a tearful goodbye, Calumon returns to his homeworld alongside the other Digimon.
Calumon returns to the Real World with the other Digimon, and ends up living with Jeri. After the defeat of Parasimon, Calumon is responsible for serving food at Rika's birthday party, and is distracted from comforting Rika by all the food on his plate. 
There are numerous products based on Calumon, including plush toys, posters, even a Tamagotchi-like game where players need to look after their own pet Calumon.
Notes and references
|Main characters:||Takato Matsuki | Henry Wong | Rika Nonaka | Ryo Akiyama | Jeri Katou | Kazu Shioda | Kenta Kitagawa | Suzie Wong | Ai and Mako|
|Digimon:||Guilmon and Grani | Terriermon | Renamon | Cyberdramon | Leomon | Guardromon | MarineAngemon | Lopmon | Impmon and Behemoth | Calumon|
|Allies:||Omnimon | Mitsuo Yamaki | Monster Makers | Digimon Sovereigns | DigiGnomes | Alice McCoy and Dobermon | Minami Uehara and Seasarmon | Takehito Uehara|
|Villains:||Hypnos | Monster Makers | Deva | Mephistomon | D-Reaper | Locomon and Parasimon | Millenniummon|
|Relationships:||Takato Matsuki | Henry Wong | Rika Nonaka | Jeri Katou | Ryo Akiyama | Kazu Shioda | Kenta Kitagawa | Suzie Wong|
|Other media:||Battle of Adventurers | Runaway Locomon | Digimon Tamers 1984 | Message in the Packet | Brave Tamer | Digimon Medley | Digimon Battle Spirit / Ver. 1.5 | Digimon Rumble Arena | Digimon Adventure|
|See also:||Digimon | Digital World | D-Power | Digi-Modify | Digital field | List of episodes|