Veles, also known as Volos, is a major god of earth, waters, livestock, and the underworld in Slavic paganism. His mythology and powers are similar, though not identical, to those of (among other deities) Hades, Loki, and Hermes.

According to reconstruction by some researchers, he is the opponent of the supreme thunder god Perun. As such, he has probably been imagined as a dragon, which in the belief of the pagan Slavs is a chimeric being resembling a cross between a bear and a snake that devours livestock. His tree is the willow, while that of Perun is the oak.^{[citation needed]} No direct accounts survive, but reconstructionists speculate that he may directly continue aspects of the Proto-Indo-European pantheon with the original deity Welnos.

Veles is one of few Slavic gods for which evidence of offerings can be found in all Slavic nations. The Primary Chronicle, a historical record of the early Kievan Rus, is the earliest and most important record, mentioning a god named Volos several times. Here, Volos is mentioned as god of cattle and peasants, who will punish oath-breakers with diseases, the opposite of Perun who is described as a ruling god of war who punishes by death in battle. In the later half of the 10th century, Veles or Volos was one of seven gods whose statues Vladimir I of Kiev had erected in his city. It is very interesting that Veles' statue apparently did not stand next to others, on the hill where the prince's castle was, but lower in the city, in the marketplace. Not only does this indicate that Veles was connected with commerce, but it also shows that worship of Perun and Veles had to be kept separate: while it was proper for Perun's shrines to be built high, on the top of the hill, Veles' place was down, in the lowlands.

A similar pattern can be observed among the South Slavs. Here the name of Veles appears only in toponyms, the best-known of which is the city of Veles in Macedonia, over which looms a hill of St. Elias the Thunderer. Also, in Bosnia and Herzegovina, a part of Sarajevo is called Velešići and a mountain Velež^{[circular reference]} near Mostar, Herzegovina. Other examples are Veles in Western Serbia, Velesnica on the Danube and Velestovo in Montenegro and also the township of Velestino (Βελεστίνο, today Φέρες), apparently bearing testimony to a Slavic layer in the settlement of Thessaly. Another debatable if not improbable example is the town of Volosko in Croatia, situated on the seashore under the peak of Mount Učka, nicknamed Perun.

Among Western Slavs, the name can be principally found in 15th and 16th century Czech records, where it means either dragon or devil.

Presumably it is not possible to conclusively determine a definite etymology for the name of the god Veles, though there are several Proto-Indo-European roots that are all closely related to the nature of Veles and his domains. Further complicating matters is the presence of Lithuanian vėlės, which Fraenkel claims is unrelated to the Slavic term. Moreover, it remains to be determined what the original shape of the lemma was in early Slavic, which obfuscates its history and linguistic relationships.

One possibility is that the name derives from the Proto-Indo-European root *wel-, meaning wool. This seems plausible, since in Slavic cosmology Veles in serpentine form is lying in a nest of black wool in the roots of the Tree of the World and Veles is the shepherd of the dead. Volos is also the Russian and Ukrainian word for "hair" and Veles is hairy in his beastly form (bear, wolf). However, since the early 20th century, since the advent of Proto-Indo-European laryngeal theory, the 'wool' word has been reconstructed as *h₂wĺ̥h₁neh₂.

The Proto-Indo-European root *welg- also means 'humid, wet'. Nothing is more connected with Veles than humidity and wetness. His domain is down, 'у воду пот корч пот колоду' ("in the water, below the tree stump and the log"). However, this etymology can be discounted, as there is no velar in Veles.