Fomorian
Fomorians are a species of giant originating from Irish mythology, characterized by their hideously deformed appearance and proclivities for dark sorcery.
In Dungeons & Dragons, traditionally, the fomorian is essentially a grotesquely ugly and evil giant that ranks even lower than the Hill Giant on the Ordning. Deformed and malevolent, they are so physically warped they can't even hurl boulders like every single other species of giant in D&D can. They are cavern dwellers whose crude tribes consist of one alpha fomorian and whatever other unfortunates he or she can bully and torment, spending their time looking for victims to torture and eat.
In 4th edition, they changed; the 4e fomorian is a fey giant, believed to be an echo of the Feywild, whose great empire once warred with that of the Eladrin. Ultimately defeated, they were exposed to magical backlashes that devastated their bodies and minds, leaving the once-beautiful giants as hideously deformed and insane monsters. 4e Fomorians are best defined by their "Evil Eyes", a large and distorted eye that serves as a focus for magical energies, allowing them to inflict all kinds of deadly magical attacks on their enemies. Too insane, paranoid and malevolent to form a cohesive threat, their petty empires still throng the Underdark of the Feywild, backed by loyal cyclops servitors and reigning over armies of slaves, such as the gnomes.
The 5e version of the fomorian is basically a watered-down version of the 4e version.