A demon of vengeance in Greek myth, and a possessing entity akin to Nemesis in Christian demonology. Spelled "Aleister," may be an allusion to purported black magician Aleister Crowley.
Anime and Manga
In Vampire The Masquerade, alastors are the Camarilla enforcers charged with hunting down and destroying the Anathema, those vampires who the Camarilla have marked for Final Death.
The Executioner of Hell in the Ninth Hell of Nessus in Dungeons & Dragons.
Though stay far FAR away from the dub, it is undoubtedly a convention for the worst voice actors ever. It's even worse than "legendary" titles like M.D. Geist and Ogenki Clinic.
It's possible that Edmond Dantes of The Count of Monte Cristo was named with this intent, given that he sentences his enemies to an Ironic Hell (albeit while still on earth).
Norse Mythology. A giant wolf, son of god Loki, fated to break free from his chains on the coming of Ragnarok and eat Odin. Also known as Fenris, Fenrisúlfr...
Literature
Fenris Wolfbrother, an orc chieftain in WarCraft II Beyond the Dark Portal.
Fenris Isle in World of Warcraft, probably not named after the orc. Home of a dark wizard and his Gnolls (hyena-like humanoids) minions until the Cataclysm expansion pack. Also Fenrus the Devourer, a gigantic wolfworg.
In Starcraft, the Jormungand Brood, controlled by the player during the Zerg campaign, and therefore responsible for the invasion of Aiur.
A gigantic serpent called Jormungandr serves as an early boss in Magicka.
Lamia
An ancient Greek demon whose description boils down to 'succubus of children.'
Anime and Manga
Also see Demon Lord Dante by Go Nagai. Lamia wants to alternatively either screw or eat everyone in the city to have/make food for her zillions of spider babies. (She's a drider instead of the typical half-snake version fantasy works usually toss up)
Also Lamia Loveless from Super Robot Wars. An android and efficient spy who will sneak into your team, get really friendly with your teammates, while leaking information to her higher ups so at one point, she will be able to bring your group down in one swift move, and she has no concern in anything except her mission, her life included. Played straight in SRW Advance, when playing Axel's scenario, whereas she never did develop her conscience and stays as a cold blooded android.
Nergal, frontman/lyricist of the Polish death-metal band Behemoth. Somewhat fitting, since their lyrics play with theosophy a lot.
Odin
Norse Mythology. Usually referred to as 'the Allfather', 'Old One-eye' or 'the Ferryman', as He's rather scary and naming Him directly might bring you unwanted attention.
Odin from American Gods, although he actually avoids using the name.
Not evil by intention, but released evil upon the world.
Anime and Manga
Gives its name to the research organization PANDORA in Darker than Black, which like Nergal in Nadesico is ostensibly good - apparently no one in either cast studied mythology.
Pandora is also the world inhabited by the Na'vi in Avatar. Not evil itself, but a foreshadowing that it won't remain undisturbed. Also fits the Greco-Roman theme naming of planets *
according to the "Manual", Pandora is a moon in the Alpha Centauri system orbiting the planet Polyphemus
The Shiva Squadron from the Feng Shui supplement Glimpse of the Abyss are a Demon SlayingAmazon Brigade with eight arms much like their namesake (they're even called "shivas"). They're also not too keen on anyone who associates with demons, even if the demon in question has joined the forces of good (like quite a few Supernatural Creature PCs).
Oda Nobunaga is often referred to as "Dairokuten Maou" literally "Devil King of the Sixth Heaven" in various franchises he appears in (a nickname he apparently chose for himself in Real Life). This is roughly the Buddhist equivalent of Satan.
Beast Wars's Megatron uses this as an invoked trope, in an attempt to be the figure from the series' equivalent of The Bible, "The Covenant of Primus". The Transformers Wiki put it best: "What distinguishes Megatron from the countless others who share [his] goal is his chutzpah. This is a guy who named himself after his faith's equivalent of the Antichrist."
Titan. If you are in a super heroes work, and you hear the name, or title, Titan, why the hell are you still around to hear it? From Dark Horse (Superman expy goes insane and decides he should rule), to Marvel (last stop in a journal belonging to a guy found floating in the air, dead, making like the human torch), to Dreamworks (a manufactured Ascended Fanboy with the nom de guerre of Titan decides he'd much rather use his powers for crime and the easy life) to any of a number of works, if something is named Titan, get the fuck away from it.
