Perkūnas (Lithuanian) and Pērkons (Latvian) was the Baltic god of thunder — the most actively mythologically articulated of the Baltic gods, perhaps because his function was the most concretely visible (every storm was his work). He was a warrior-figure in red armor, riding through the heavens with hammer and axe, hurling stones at the demons and the trees of the dark spirits below. His enemy was Velnias (treated below), the chthonic-and-underworld figure whom Perkūnas pursued through every storm — a striking parallel to the reconstructed Slavic Perun-Veles cosmic conflict, suggesting an inherited Indo-European storm-god-vs.-chthonic-adversary myth. Perkūnas's name corresponds etymologically to Slavic Perun, Vedic Parjanya, and possibly to the Norse Fjörgyn (Thor's mother).

His sacred tree was the oak, struck by lightning more often than other trees; his cult-images stood in oak-groves; his sacred fire was kept by priestesses (the Vaidilutės) in his sanctuaries, of which the most famous was at Romove in pre-Christian Prussia. He was widely honored across the Baltic territories, and his cult was substantial enough that the Christianization of the Balts had to make special provision for the suppression of his sacred groves. The Baltic peasants continued to invoke him after the conversion, with Saint Elijah of the Old Testament becoming his Christian-period substitute (parallel to Slavic Saint Elijah-as-Perun).