Apocalymon

Apocalymon is the main and final antagonist of Digimon Adventure. He is Mega Digimon.

Digimon Adventure
In Now Apocalymon,

In The Fate of Two Worlds,

Trivia

 * Apocalymon's name comes from the word "apocalypse" which is synonymous with the end of the world.
 * Apocalymon's design is often speculated by fans to be based on Winslow Leech from the 1974 film Phantom of the Paradise.