Omnimon

Omnimon is a character in the Digimon series and is one of the Thirteen Royal Knights. He was known as Omegamon in the Japanese version, and is the result of a fusion between WarGreymon and MetalGarurumon. The head of each became fused onto Omnimon's arms, enabling him to use two attacks: Transcendent Sword (Grey Sword in Japan) with the WarGreymon arm, and Supreme Cannon (Garuru Cannon in Japan) with the MetalGarurumon arm. Somtimes considered the most powerful digimon of all.

Our War Game
Omnimon was formed from the energy of Tai and Matt when their respective digimon proved unrespondive in the Digital World. Both Tai and Matt digitalized into the computer world by accident, and helped their Digimon fuse into Omnimon to defeat Diaboromon. Izzy redirected thousands of other childrens's supportive emails at Diaboromon to give him massive lag, and Omnimon was able to defeat him and deactivate the nuclear missiles Diaboromon had hacked into and sent to Japan and Colorado.

Revenge of Diaboromon
Three years later, when Diaboromon was discovered to have survived, Omnimon went into 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 final blow with his Transcendent Sword, essentially destroying Diaboromon, but it was a trap for all of the Kuramon to get through to the real world. The Kuramon formed Armageddemon, and Omnimon was able to follow it the real world to deal with it, but despite his best efforts Omnimon was no match for Armageddemon, and his arms were separated from his body. In the end Omnimon gives the rest of his energy to Imperialdramon Fighter Mode, creating Imperialdramon Paladin Mode, where his main body transforms into the Omni Sword (Omega Blade in Japan) while the arms revert back to Agumon and Gabumon.

Battle of the Adventurers
Omnimon later appeared in a fifth Digimon movie, though it was a different Omnimon whose mission was to stop the movie's antagonist, Mephistomon, from entering the real-world to kill every human in it. Unfortunately, Omnimon failed, and had to assemble Takato, Rika and Henry to fight Mephistomon for him, as Omnimon had to destroy the other evil Digimon taking advantage of the crisis.

V-Tamer
Omnimon is the third mega Digimon Zeromaru had to fight, the partner of Hideto Fujimoto of the Alias Three, made up of Org the WarGreymon and Meruga the MetalGarurumon. After being defeated by Zeromaru, Omnimon would later help him out in the fight against Arcadimon. He is the only Digimon of the Alias Three that wasn't destroyed.

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 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 an X-Antibody that the Knight's eyes were really opened to Yggdrasil's true motives. Transforming into Omnimon X, he destroyed Yggdrasil with All Delete, resetting the Digital World as a result.