In Christian demonology, Alastor is chief executioner to the monarch of Hell.
According to Dictionnaire Infernal - Collin de Plancy (1863), Alastor is likened to Nemesis and the destroying angel and is known as The Executioner. He is exceptionally cruel.
- Alastor ("avenger") in Greek mythology, was the personification of familial feuds. He was also associated with sins that pass down from parent to child. As a genius, or spirit of the household in Roman mythology, he incited people to murder and other sins. The name became a generic term for a class of evil spirits.
- Plutarch says that Cicero hated Augustus so much that he conceived of a plan to kill himself outside Augustus' foyer, in order to become his alastor.
Sometimes he resolved to go into Cæsar's house privately, and there kill himself upon the altar of his household gods, to bring divine vengeance upon him; but the fear of torture put him off this course. verse 68 of Cicero's bio in Plutarch's Parallel Lives
- Another Alastor was a mortal, son of Neleus, King of Pylos. He was later downgraded to a minor daemon after he and his brothers were killed by Heracles.
- Last but no least, Alastor was friend of Serpedon, who was killed by Odysseus.
- Percy Bysshe Shelly wrote a poem (Alastor or The Spirit of Solitude - 1816), which warned idealists that if they are always searching for an ideal love, the world will be their tormentor, and they will die a lonely death.
- Edward Alexander Crowley, 20th century ceremonial magician, changed his first name to Aleister. The difference in spelling can be easily attributed to the fact that 'Alastor Crowley' does not add up to 666.
- Alastor is also a quasi-sentient sword and a winged devil in the first Devil May Cry game by Capcom. His first appearance is a scene where the sword moves on its own, stabbing the protagonist Dante through the chest. In the game, Alastor has his own will, but is overpowered by Dante, and becomes his primary weapon for most of the game; the spirit of Alastor warns Dante of impending danger via an electric surge through the blade.
- Alastor also appears in a more active role and with a slightly different appearance in all of the Viewtiful Joe games, also by Capcom. In most of the Viewtiful Joe games he serves as a 4th level boss, and sometimes as a playable character. He has a Devil Trigger form much like Dante's, and a conversation between the two characters in the PlayStation 2 version of Viewtiful Joe confirms that he is the same devil that animated the Alastor sword in Devil May Cry. He has somehow escaped the sword, but still uses it as his own weapon.
- Alastor has also appeared as an enemy in the famous Konami series, Castlevania, specifically in Castlevania: Aria of Sorrow. He appears as a translucent silhouette of a Demon with its only visible feature being a broken dark sword. Earning Alastor's soul in that game grants the user the summoning of Alastor's Sword as a Familiar that follows the user and attacks in tandem. He returns in Castlevania: Portrait of Ruin again his only visible feature being a sword, but instead of becoming a familiar (as they are not present in this game) there is a very small chance that you can obtain his "damascus sword" after killing him.
- Alastor has also appeared as the leader of Hell's army in Painkiller, and the final boss in Battle out of Hell, the first Painkiller addon. He appears as a towering winged demon with massive jaws in Painkiller, and a heavily armoured version of said demon in Battle out of Hell.
- In the role-playing game Vampire: The Masquerade by White Wolf Game Studio the Alastors are an elite group of enforcers (Archons) of the Camarilla whose sole responsibility is tracking and destroying the Anathema (those listed on the Red List).
- Alastor's Hood -- late-game headgear in Golden Sun: The Lost Age; this hood can be used in battle "to Haunt a foe."
- "Tenjo no Goka" Alastor: He is the Crimson Lord to whom Shana, of Shakugan no Shana, is bound.
- Alastor makes an appearance as a mini-boss in the PC game Titan Quest. He is referred to in-game as "The Scourge of Acheron."
- In the Dungeons & Dragons roleplaying game, Alastor is the grim, silent pit fiend who serves as the Executioner of Baator. He is also the bodyguard of the Dark Lord of Nessus and is that power's most trusted servant.
- Alastor Moody is a character appearing in the Harry Potter series by JK Rowling
- Jack Vance wrote three loosely related novels set in a fictitious globular cluster called Alastor.
- A poem by Percy Bysshe Shelley is named “Alastor, or The Spirit of Solitude”
- Alastor plays his demonic self in “Night Play”, a Dark-Hunter novel by Sherrilyn Kenyon, where he is called upon by Were-Hunters to cause mischief. Bryani, Vane's mother, conjures Alastor to bring Bride back in time to Dark Age Britain.
- Alastor, Russian composer Nikolai Myaskovsky's 1912 symphonic poem (Op. 14) based on Shelley's poem.
- Alastor is also the name of a now-defunct Atlanta rock band, who released three critically-acclaimed albums: “Javelin Catcher” (1997), “Nothing for Anyone” (1999) and “The Late Night Plays” (2002). Alastor's lead singer Elizabeth Elkins went on to the more commercially-appealing, and arguably stronger rock outfit “The Swear” .