Mephistomon

Mephistomon is an evil Digimon (From the Digimon fictional universe) born from the remains of Apocalymon.

Like his 'father'/predecessor Apocalymon, Mephistomon had a deep hatred for all life and plotted the death and destruction of the world and all living things in it. To accomplish this purpose, he took on the alias of Ryuuji Tamashiro, the young president of a new Okinawan venture enterprise, VP Laboratories. He became famous for creating the V-Pet, a popular pet software that served to bring other Digimon as evil as Mephistomon to the human world.

He eventually revealed himself when he found the location of the Vaccine program that would undo his plans. In order to destroy this Vaccine program, he had to deal with the Tamers, eventually dragging them and everyone else under the oceans and into a post-apocaliptic dimension modeled after what he intended for the real world. After he was defeated and the Vaccine program ran its course, Mephistomon digivolved to Gulfmon, and was defeated and destroyed.