Dark Gods

Dark Gods are a common archetype found in fantasy settings - though similar beings can be found in other genres as well, it is especially common in a "Rage Against the Heavens" plot in which the hero(es) of a story must fight against the power of an evil and/or uncaring god (sometimes even God himself (see God as Satan).

Since there were no true gods of "evil" in mythology, the usual candidates for Dark God status in modern tales are gods of the underworld or pagan deities of considerable fame - this can be confusing when looking at the older myths as many underworld deities were benevolent and/or amoral, it is theorized a lot of the negative traits of death-gods in the modern mind stems from the way death has become a symbol of evil while in the past it was (largely) considered a natural part of existence.

Trickster gods are also common candidates for this archetype and indeed in real-world mythology a number of trickster gods have shown traits that can be considered malevolent - such as Loki and some varieties of the Coyote.

Dark Gods tend to be portrayed as keeping their divine status and role (unlike demons) and even though many Dark Gods display traits and abilities associated with demons they are normally still in contact with other gods and have people who worship them: in some settings however the term "demon" can apply to fallen gods just as it traditionally applied to fallen angels.

Dark Gods In Fiction

Live-Action Films

Gozer (Ghostbusters).
Loki (Son of the Mask).
God (The Acid House: The Granton Star Chase).
Hades (Clash of the Titans).
Kronos (Wrath of the Titans).
Set (Gods of Egypt).
Marvel Cinematic Universe:
- Loki
- Hela
- Surtur
- Dormammu

Animation

Hades (Disney’s Hercules).
Eris (Sinbad).
Te Kā (Moana).
Satan (South Park).

Comics

Darkseid (DC Comics).
Marvel:
- Loki Laufeyson, better known as Loki
- Hela
Satan (Spawn).

Anime/Manga

Dragon Ball series:
- Broly
- Beerus
- Champa
- Zen-Oh
- Zamasu/Goku Black
Kaguya Ōtsutsuki (Naruto).
Isshiki (Boruto: Naruto Next Generations).
Fullmetal Alchemist Brotherhood:
- Truth
- Father
Death Note:
- Ryuk
- Shinigami King
Asura (Soul Eater).
Master of Hell (Jigoku Shoujo).
Homura Akemi (Puella Magi Madoka Magica).
Future Diary:
- Deus Ex Machina
- Yuno Gasai
Gods (Unico).

Video Games

Mortal Kombat:
- Lord Shinnok (Mortal Kombat Mythologies: Sub-Zero).
- Dark Kahn (Mortal Kombat vs. DC Universe).
- Lady Kronika (Mortal Kombat 11).
- The Titans (Mortal Kombat 11).
Bendy (Bendy and Ink Machine).
Lucifer (Dante's Inferno).
Zeus (God of War).
Kid Icarus:
- Hades
- Medusa
Sinistrals (Lufia).
Lord Er (Seraphic Blue).
Hades (Valkyrie Crusade).
The four Chaos Gods, Tzeentch, Nurgle, Slaanesh, Khorne (Warhammer).
Zeus (Will Rock).

Others

Teridax (BIONICLE).

Dark Gods In Mythology

Cronus/Kronus (the titan who fathered the Olympians is famous for his mad quest to stop Zeus from taking his throne - by devouring his own young.)
Zeus (although revered as the chief deity of the Olympian pantheon Zeus was infamous for his many abuses of power, which caused trouble between the gods and mortals - he was also instrumental in the creation of the Minotaur.)
Hera (mother of the Olympian pantheon and consort to Zeus, she was infamous for her jealousy and tendency to curse anyone who angered her, but in fairness to Hera most Olympians were just as petty as she was and much of her anger came from Zeus' abuse of power.)
Ares (in mythology Ares was not so much the god of war, but as the god of slaughter with all the negativity that came with it.)
Eris (the goddess of chaos, strife and discord in Greek mythology, who was the main responsible for causing the events that leaded to the Trojan War.)
Fomorians (while possessing same reputation with trolls, giants, and ogres (mystical races that analogous to them in popular culture) and more than often depicted as such on a first glance, Fomorians are Dark Gods which represents darker aspect of nature and has tempestuous command over it, with Tuatha Dé Danann being the only ones who can match their strength.)
Jötnar (on the same vein with Fomorians, contrary to popular culture's designation of them as analogous to giants, trolls, and ogres, Jötnar (singular Jötunn) are actually Dark Gods representing destructive and harmful aspects of nature which placated instead of worshipped, making them dark counterparts of Gods of Asgard.)
- Loki (the Norse trickster god is often considered a charming rogue - until his mischief-making causes him to cross the Moral Event Horizon and become, in essence, the Norse equivalent to Lucifer.)
Set (once a desert-god of Egypt, this infamous deity devolved into a hateful embodiment of chaos over the years.)