From World of Warcraft.
While the overall concept of orcs draws on a variety of pre-existing mythology, the main conception of the creatures stems from the fantasy writings of J. R. R. Tolkien, in particular The Lord of the Rings. In Tolkien’s works, orcs are a brutish, aggressive, repulsive and generally malevolent species, existing in stark contrast with the benevolent Elvish race (from which their own ancestors may have been developed and corrupted) and generally pressed into the service of an evil power. Tolkien’s concept of orcs has subsequently been adapted and imported into other works of fantasy fiction as well as into fantasy role-playing and strategy games (such as Dungeons & Dragons, Warhammer and Warcraft), broadening the recognition of the creatures in popular culture.
Earlier references to creatures etymologically or conceptually similar to orcs can be found in Old English and Anglo-Saxon sources; including Beowulf and 16th-century Italian folk tales, in particular those of Giambattista Basile.