Apocalymon

Arguably one of the strogest Digimon ever known, Apocalymon was born from the assimulated data of every Digimon that was "destoryed" by the DigitalWorld's evolution. A sadistic & tormented soul, Apocalymon wanted to make the Digital World a living hell to justify those who compose him. It took a combined force of Wargreymon, MetalGarurumon, Garudamon, Megakabuterrimon, Lilymon, Zudomon, Magna Angemon, and Angewomon to defeat him. But when he tried to commit sucide/genocide with his self-destruct Total Annilation, the DigiDestined sealed him with their Digivices so he would only kill himself.

Apocalymon would later appeared Fifth Digimon Movie (Not released in America), though it is a different Apocalymon, he was very much like last one. But when he was seemingly killed by Omnimon, Apocalymon's data reformed into a new evil to carry out his justice, Mephistomon.