The Fantastic Four's Enemies
First introduced in Issue #5, Dr. Doom is the Fantastic Four's eternal arch foe. An evil genius, he was one of Reed and Ben's college classmates. He was interested in the occult, and one of his experiments resulted in a large explosion which left his face hideously scarred (see Issue #278 to see his scar). He then exiled himself, and created his armor and face mask to hide his scarring. Doom has "died" several times, most recently in Issue #260, and Issue #381 along with Reed. He often brags about his genious, while refusing to admit Reed's comperable genius. Though he is evil, he is also a man of his word, a fact which the FF have found useful several times. Doom is the "monarch" (dictator) of Latveria, a small country which he tries to use to conquer the rest of the world. The capital of Latveria and the location of Doom's castle is Doomstadt (from German : Doomtown).
Aron, like Uatu, is a Watcher invested with the power cosmic. Also
like Uatu, he often disregards his vow of noninterference, and has
tried to conquer the unvierse. Aron was killed by Uatu in Issue
#400.
The Beyonder is not really an enemy, but more of a menace. First
introduced in Secret Wars I #1, the Beyonder is "from beyond".
He is all that exists in his universe, and thusly has incredible
powers. In the first Secret Wars, he kidnapped many of the Earth's
super heroes and super villians, and placed them upon the Secret
Wars planet, where he told them that if they defeated each other,
that all they desired would be theirs. The fact that the Beyonder
can change anything he wants at his whim is what makes him so
dangerous.
Devos was first introduced in Issue #359.
Aron the Rogue Watcher
The Beyonder
Devos the Devastator