In Incarnate Forme, Thundurus is a blue, muscular humanoid Pokémon, which resembles a genie. It is a male-only species with no female counterpart. On its head is a single, long, sharp, purple horn. Thundurus has white, zigzagging and jutting styled hair, a spiky white mustache and two pointed blue ears on either side of its head. Its eyes are yellow with beady white irises and no visible pupils. The front of Thundurus's body is covered in various, irregularly shaped purple spots. Its broad chest consists of two joined, purple, rounded-diamond shaped pectorals and its shoulders, elbows and navel are adorned with raindrop like designs. It has two spotted muscular arms, with five fingers on each hand. Its lower body consists of a trailing cloud, with a thick, long, curling, purple, cable-like tail. Spanning the length of its tail, Thundurus has several ball-like structures. They are a dark gray color, and each has a long, sharp spike on one side.
In Therian Forme, Thundurus is a large, blue, sleek, bipedal snake or dragon-like Pokémon. The horn on its head is now thicker and extends out more, while its ears become more pointy and pinned back. Thundurus's hair remains the same; the mustache now takes on a more raised snout and fanged-maw-like appearance, with two curving wisps flowing back and past its ears. Its eyes remain yellow, but with larger irises which still lack visible pupils. Its chest remains broad and unchanged, while its navel is bejeweled with a blue gem. Thundurus's arms have lost much of their muscular bulk, and are now slimmer. It has two paw-like hands, each covered in a trailing cloud-like fluff and with three claw-tipped fingers. Thundurus's purple lower half is much smaller than its upper body, and consist of two hind-legs and its tail. Its feet are elongated, with three downward curved toes and claws. Thundurus's tail also remains largely unchanged, although it is thicker at the base and tapers off and becomes thinner toward the tip.
Thundurus made his first appearance in Nimbasa City, where he shocked Black after the Nimbasa Gym's roller coaster was sabotaged and forced him to the Gym's roof. Later, Thundurus got in a battle with Tornadus near the Battle Subway. After being stopped by Landorus, the three were captured by Giallo for Team Plasma to use. Later they were used by the Shadow Triad against the Gym Leaders. These Pokémon were than given to Hood Man (Colress) to experiment how to change them to their alternate forms. He first appeared in Battle on a Roller Coaster.
In Incarnate Forme, Thundurus is based on Raijin, the kami of thunder and lightning. It may also have drawn inspiration from genies.
In Therian Forme, Thundurus seems to be based on a reptile, most likely a snake or dragon. It may also draw inspiration from the Azure Dragon and/or Black Tortoise of the Chinese Four Symbols constellation; or from Quetzalcoatl, a god from the Aztec mythology that resembles a feathered serpent. It also may be based on the Qiling, a mythical creature from east Asia described to have a horn on its forehead and occasionally associated with lightning.
Thundurus is from thunderous and possibly Aeolus, ruler of the winds in Greek mythology.
Voltolos is derived from volt and Αἴολος Aiolos (Greek name for Aeolus).