Good vs. evil
The conflict of good against evil is a theme in the many popular forms of fantasy; normally, evil characters invade and disrupt the good characters' lands. J. R. R. Tolkien delved into the nature of good and evil in The Lord of the Rings, but many of those who followed him use the conflict as a plot device, and often do not distinguish the sides by their behavior. In some works, most notably in sword and sorcery, evil is not opposed by the unambiguously good but by the morally unreliable.
Heroic characters are a mainstay of fantasy, particularly high fantasy and sword and sorcery. Such characters are capable of more than ordinary behavior, physically, morally, or both. Sometimes they might have to grow into the role ordained for them. This may take the form of maturation, which is often through Coming of Age.
Many protagonists are, unknown to themselves, of royal blood. Even in so fanciful a tale as Through the Looking-Glass, Alice is made a queen in the end; this can serve as a symbolic recognition of the hero's inner worth. Commonly, these tales revolve around the maltreated hero coming into his or her own. This can reflect a wish-fulfillment dream, or symbolically embody a profound transformation.
The forces of evil are often personified in a "Dark Lord". Besides possessing vast magical abilities, a Dark Lord often controls great armies and can be portrayed as possessing devil-like qualities. A Dark Lord is usually depicted as the ultimate personification of evil, as with Sauron of The Lord of the Rings; Conan the Barbarian's archenemy, Thulsa Doom; the Dark One (Shai'tan) of The Wheel of Time; and the Sith Lords from Star Wars, which include Darth Vader and Emperor Palpatine.
Other notable Dark Lords include: Lord Voldemort of Harry Potter; Darkseid from DC Comics; Thanos from Marvel Comics; Mundus from the Devil May Cry video game series; Dracula of the Castlevania series; Skeletor from Masters of the Universe; Morgoth from The Silmarillion; Arawn Death-Lord from The Chronicles of Prydain; Torak from The Belgariad; Nightmare from Soulcalibur; Ganon from The Legend of Zelda; Exdeath from Final Fantasy V, and Galbatorix from The Inheritance Cycle. The villain of the Demon Sword video game is also literally called Dark Lord.
In the Lone Wolf gamebooks, the Dark Lords are a race of powerful evil beings. The protagonists of the Overlord video game franchise are classic Dark Lords in the vein of Sauron. The Dark Lord is usually seen as unmarried, though there has been the occasion when one has attempted to claim a bride.