Veles, also known as Volos or Weles, was the slavic god of the underworld called Nav, who also had claim on the earth and waters.
He is deity of discord who opposes Perun, the lord of skies and chief of the slavic pantheon, and the clash between the two deities is a key component in slavic mythology and an occurrence of the Chaoskampf. Veles is sometimes even depicted as either a serpent or Dragon, which fits the motive of the Chaoskampf.
Veles also governed the underworld as a fair ruler, with the souls of the dead serving as shepherd for his herds of sheep on a fresh and fertile plane.
He was also considered a trickster deity, as well as a patron for the musicians and practitioners of magic.