Fire Giants are one of the six "core" breeds of Giant in the worlds of Dungeons & Dragons. As their name suggests, they are a borderline elemental species, heavily associated with volcanoes - and to a lesser extent other areas of extreme heat, such as deserts. This elemental nature shines through in both their immunity to fire and their coloration; they tend to have dark skin on a coffee-to-ashen-purple spectrum and (naturally) bright red hair - assuming it's not on fire.
Like Frost Giants, fire giants originate from Norse Mythology, where they were associated with the Realm of Fire, Muspelheim. Unlike their icy kin, fire giants are associated less with vikings and more with dwarves; they are an evil race best known for their skills at crafting metal and stone, using their fiery homes to help produce masterworked weapons or armor, and even enchanted gear. They are often even described as having similar bodily proportions to dwarves - you know, except for being 20+ feet tall. In some ways, they are the most civilized of the "usually evil" breeds of giant, although they are still tyrants and slavers whose society can best be described as "cut-throat".