Omnimon

A character in the Digimon series, Omnimon is of the Thirteen Royal Knights, he was known as Omegamon in the Japanese version. He is the result of a fusion between War Greymon and MetalGarurumon(Both their bodies become Omnimon's Arms).

First Season (Digimon Adventure): Our War Game
He was formed from the postive energy of children when Taichi Yagami and Yamato Ishida both digitalized into the computer world so that they could help their Digimon stop Diaborromon. With a little help from Koushiro who redirected the other childrens email at Diaborromon to slow him down, Omnimon is able to kill him and deactivate the nuclear missiles that were headed for Japan.

Second Season (Digimon 02): Diaborromon's Revenge
Three years later, when Diaboromon was discovered to have survived, Omnimon went to the internet to deal with him once again. With some help from Angemon and Angewomon who helped distract Diaboromon and hold him down Omnimon was able to administer the Coup De Grace with his Transcendent Sword destroying Diaboromon, but it was all a trap for all of the Kuramon to get through to the real world which then formed Armageddemon. Omnimon was able to follow to the real world as well to deal with Armageddemon but despite his best efforts Omnimon was no match for him and his arms were separated from his body. In the end Omnimon gives the rest of his energy to Imperial Dramon Fighter Mode creating Imperial Dramon Paladin Mode where his main body transforms into the Omega Sword (Omega Blade) while the arms revert back to Agumon and Gabumon.

Digimon Tamers Movie
Omnimon later appeared Fifth Digimon Movie (also not released in America), though it is a different Omnimon, whose mission was to stop the movie's antagonist, Mephistomon, from entering the real-world to kill every human in it. But Omnimon failed and had to assemble Takato Matsuda, Ruki Makino, and Jenrya Li to fight Mephistomon for him as Omnimon had to destroy the other evil Digimon taking advantage of the crisis.

Digimon V-Tamer
The third mega Digimon Zeromaru had to fight, the partner of Hideto of the Allias Three. After being defeated by Zeromaru, he would later help him out in the fight against Arcadimon.

Digimon X-Evolution
He is the confident leader of the Royal Knights, initially carrying out Project Ark almost to the letter. He is a follower of the word of Yggdrasil, a super-computer governing the current Digital World. In X-Evolution, he is the main policing power, although he acts against informants and those betrayed with unprejudiced force. When Gallantmon confronted him about Yggdrasil, they were unable to agree about the nature of Project Ark and so they fought, ending with the other Knight's demise. This event is what makes Omnimon seriously start to question Yggdrasil, shaken as he is by his friend's death. But even so, he still carries out Yggdrasil's orders.

It was only when Alphamon saved Omnimon's life, and gave him a X-Antibody in the process, the the Knight's eyes were really opened to Yggdrasil's true motives. X-digivolving into Omnimon X, he destroyed Yggdrasil with All Delete, resetting the Digital World as a result.