Lord Devimon is the first major villain to face the DigiDestined, and is responsible for enslaving File Island with his Black Gears, hiding the Tags and Crests, and attacking the children directly and indirectly multiple times. Devimon controls the Black Gears, which perform multiple tasks for him. He generally uses free ones that when summoned will fly towards and eventually collide with a Digimon, bending it to his will Biyomon Gets Firepower and, sometimes, increasing its power and size, especially if the target is struck by multiple gears. The Legend of the DigiDestined There are also some that will serve as scrying mirrors to keep watch on the children. DigiBaby Boom Another set of Black Gears are built into giant arrays as the core of File Island itself. When operated, they can cause the pieces of File Island to separate from or rejoin Infinity Mountain. Evil Shows His Face Although Devimon has a strong control over the Black Gears, and at one point it is stated that Devimon didn't create the Black Gears but mainly found them on File Island.
Prior to Digimon Adventure
Before the events of the series, Devimon takes control of File Island. At some point he finds a prophecy that says the DigiDestined will destroy him, and so he hides their Tags and Crests across the continent of Server. Departure for a New Continent Although it is never specifically mentioned, it is possible that Devimon received the tags and crests from Piedmon, who had originally stolen them from Gennai before the start of the series.
When the DigiDestined arrive on File Island, he indirectly attacks them with Black Gear infected Digimon and puts the renowned Leomon and Ogremon under his thrall. The children eventually climb Infinity Mountain and reach his mansion. There, he gives the DigiDestined an amazing dinner and a nice, hot bath in a sauna—all of which are designed to lull them into a false sense of security so that he can strike while their guards are down. He splits the island using his Black Gears and separates the DigiDestined, but his attempts to kill Taichi "Tai" Kamiya are stopped when his Digivice frees Leomon from his spell
Unfortunately, the DigiDestined manage to find ways to return the pieces of the island to their original state. As he observes Takeru "T.K." Takaishi's resolve to fight, Devimon knows that he has to kill him and his partner Patamon before they can digivolve to the Champion level. DigiBaby Boom To this end, he sends Leomon and Ogremon to kill the pair, who are then saved by T.K.'s brother Yamato "Matt" Ishida, Tai, and their Digimon Garurumon and Greymon. When Leomon seems to be losing, he sends more Black Gears to power Leomon with darkness. Using the light of their Digivices, however, Tai and Matt banish both the Black Gears and Devimon's own influence, as the Digimon force Ogremon into retreat.
Unfortunately, all of this is to according to his plan. Leomon leads them directly to him, where he has absorbed a large amount of Black Gears, as well as Ogremon, to increase his size and strength. Now standing nearly as tall as a mountain, he shrugs off the Champion Digimon's attacks and tears through the ranks, effortlessly flinging them away. With the rest of the Digimon incapacitated, Devimon turns his attention toward T.K., whom the prophecy says will defeat him. Attempting to crush him in his hand, Patamon instead interrupts and digivolves into Angemon. Angemon deletes him with a "Hand of Fate" empowered by the light of the Digivices and Angemon's life. Though Devimon is defeated, he reveals that there are many other evil Digimon just as powerful as he is along others that are even more powerful, and gloats that even Angemon will not be able to handle them, as he cannot even defeat Devimon without sacrificing himself
Digimon Adventure 02
Devimon briefly reappears while the Digimon Emperor is searching for the piece needed to bring Kimeramon to life. When the Emperor finds the Dark Whirlpool and goes down into it to find the piece, he finds the broken remains of Devimon. The Emperor disregards Devimon's taunt-like warning that "the powers of darkness cannot be controlled" and harvests his data for what become the arms and Digi-Core of Kimeramon. An Old Enemy Returns However, Devimon's influence causes Kimeramon to rebel against the Emperor, and his voice returns to taunt him again until Kimeramon is destroyed, and Devimon's data with him.