In Slavic mythology, Perun (with many spelling and pronunciation variants among modern Slavic languages) is the highest god of the pantheon and the god of thunder and lightning. His other attributes were the mountain, oak, eagle, firmament (in Indo-European languages this was joined with the notion of the sky of stone), horses and carts, weapons (the hammer, axe and arrow), war, and fire. He was first associated with weapons made of stone and later with those of metal.
Of all historic records describing Slavic gods, those mentioning Perun are the most numerous. As early as 6th century, he was mentioned in De Bellum Gothicum, a historical source written by the Byzantine historian Procopius. A short note describing beliefs of a certain South Slavic tribe states they acknowledge that one god, creator of lightning, is the only lord of all: to him do they sacrifice an ox and all sacrifical animals. While the name of the god is not mentioned here explicitly, the fact that word Perun in a number of Slavic languages today simply means "thunder" or "lightning bolt" is proof enough this was a reference of him.
The first source that definitely mentions a god named Perun is the Rus' Primary Chronicle, a history of early Kievan Rus. Together with a god named Volos he is sworn upon in peace agreements between Slavic overlords and Byzantine emperors. Here he is mentioned as a god of war and nobility, who punishes oathbreakers with death in battle. In 980, when prince Vladimir the Great came to throne of Kiev, he erected statues of six or seven pagan gods in front of his palace. Perun was chief among these, represented with a silver head and a golden moustache. Vladimir's uncle Dobrinja also had a shrine of Perun established in his city of Novgorod. After the Christianization of Kievan Rus, this place became a monastery, which, quite remarkably, continued to bear the name of Perun.
Perun is not mentioned directly in any of the records of Western Slavic paganism, but a reference to him is perhaps made in a short note in Helmod's Chronica Slavorum, written in latter half of the 12th century, which states (quite similary to Procopius some six centuries earlier) that Slavic tribes, even though they worship many various gods, all agree there is a supreme god in heaven which rules over all other on earth. This could be a reference to Perun, but since he is not named, nor any of his chief attributes (thunder or lightning) mentioned, we cannot be certain.
Moreover, the name of Perun is also commonly found in Southern Slavic toponymy. There are places called: Perun, Perunac, Perunovac, Perunika, Perunička Glava, Peruni Vrh, Perunja Ves, Peruna Dubrava, Perunuša, Perušice, Perudina and Perutovac. These names today mostly represent mountain tops, but in medieval times, large oaks, sacred groves and even entire villages or citadels were named Perun. Also, as mentioned already, in Ukrainian perun and in Polish piorun means "thunderbolt". Among South Slavs, a mountain plant Iris germanica is known in folklore as perunika ("Perun's plant") and sometimes also as bogisha, ("god's plant"), and was believed to grow from ground that had been struck by lightning.
Perun is strongly correlated with the near-identical Perkūnas/Perkons from Baltic mythology, suggesting the existence of an ancestral Balto-Slavic deity, which ultimately derives from the Proto-Indo European thunder god whose original name has been reconstructed as Perkwunos. The root *perkwu originally probably meant oak, but in Proto-Slavic this evolved into per- meaning "to strike, to slay".
In Slavic mythology, much like in Norse mythology, the world was represented by a sacred tree, usually an oak, whose branches and trunk represented the living world of heavens and mortals, whilst its roots represented the underworld, i.e. the realm of dead. Perun was a ruler of the living world, sky and earth, and was often symbolised by an eagle sitting on the top of the tallest branch of the tree, from which he kept watch over the entire world. Deep down in the roots of the tree was the place of his enemy, symbolised by a serpent or a dragon: this was Veles, watery god of the underworld, who continually provoked Perun by stealing his cattle, children or wife. Perun pursued Veles around the earth, attacking him with his lightning bolts from the sky. Veles fled from him by transforming himself into various animals, or hiding behind trees, houses or people; wherever a lightning bolt struck, it was believed, this was because Veles hid from Perun under or behind that particular place. In the end, Perun managed to kill Veles, or to chase him back down into his watery underworld. The supreme god thus reestablished the order in the world which had been disrupted by his chaotic enemy. He then returned to the top of the World tree and proudly informed his opponent down in the roots:Ңy, таm твое место, таm сабе бyдз! ("Well, there is your place, stay there!"). This line came from a Belarusian folk tale of great antiquity. To the Slavs, the mythological symbolism of a supreme heavenly god who battles with his underworldly enemy through storms and thunder was extremely significant, and from Perun and Veles, this idea of cosmic battle was passed onto God and the Devil following Christianization.
In the classification scheme of Georges Dumézil, Perun was the god of the second function (physical and military power), a god of war, and as such, he was armed with several fantastic weapons. Perun's lightning bolts were believed to be stones and stone arrows. According to folk beliefs, fulgurites and belemnites and sometimes even remains of prehistoric stone tools found in the ground are remains of these weapons. Various Slavic countries also call these deposits "Perun's stones", "thunderbolt stones", "thunderbolt wedges" and "Perun's arrow"; other unrelated names for these include "devil's finger", "God's finger", and "Mother of God finger", and in Lithuania, "Berkun's finger". These thunderbolt stones were sometimes said to be transferred back to the sky by the wind after being under earth for a period of seven years. The weapons of Perun protected against bad luck, evil magic, disease, and - naturally enough - lightning itself.
Perun also had another type of weapon in his arsenal, as destructive as his firestone arrows, but even more unusual: mythical golden apples. While this may not seem to be much of a weapon, in many Slavic folk accounts, the golden apple appears as a talisman of ultimate destruction. An example from a Serbian folk song with strong mythical elements relates:
... Te izvadi tri jabuke zlatne
I baci ih nebu u visine...
...Tri munje od neba pukoše
Jedna gađa dva djevera mlada,
Druga gađa pašu na dorinu,
Treća gađa svata šest stotina,
Ne uteče oka za svjedoka,
Ni da kaže, kako pogiboše.
"...Then he took out three apples of gold
And threw them high into the sky...
...Three lightning bolts burst from the sky,
One strikes at two young brothers-in-law,
Another strikes at pasha on a horse,
The third strikes six hundred wedding guests,
Not an eye for a witness fled
Not even to say, how they ended dead."
It is conjectured that mythical golden apples of Perun were symbols of a rare but notorious form of atmospheric discharge, ball lightning. The same is probably true for the thunder marks of East Slavic folklore, of which two examples are shown above.
Similarly to Perkunas of Baltic mythology, Perun was considered to have multiple aspects. In one Baltic song, it is said there are in fact nine versions of Perkunas. Remains of an ancient shrine to Perun discovered beneath medieval Peryn skete in Novgorod consisted of a wide circular platform centred around a statue, encircled by a trench with eight apses, which contained sacrificial altars and possibly additional statues. The overall plan of the shrine shows clear symbolism of the number nine. This is sometimes interpreted that Perun, in fact, had nine sons (or eight sons, with himself, the father, being the ninth Perun). It should also be noted that in some Slavic folk songs, nine unnamed brothers are mentioned.
From comparison to Baltic mythology, and also from additional sources in Slavic folklore, it can alo be shown that Perun was married to the Sun. He, however, shared his wife with his enemy Veles, as each night the Sun was thought of as diving behind the horizon and into the underworld, the realm of the dead over which Veles ruled.
Like many other Indo-European thunder gods, Perun's vegetative hypostasis was the oak, especially a particularly distinctive or prominent one. In Southern Slavic traditions, marked oaks stood on country borders; communities at these positions were visited during village holidays in the late spring and during the summer. Shrines of Perun were located either on top of mountains or hills, or in sacred groves underneath ancient oaks. These were a general place of worship and holding of sacrifices (with a bull, an ox, a ram, and eggs). It seems humans were also sacrificed to Perun. According to the Primary Chronicle, prisoners of war were sacrificed to him, probably one each year, during the nine days of his holy festival, which was held in mid-summer.
With the arrival of Christianity, various churches had a difficult time trying to overcome the worship of the old supreme deities of the Slavs. In the East, the Eastern Orthodox Church gradually managed to pass much of Perun's characteristics on to a new Christian saint, Elias the Thunderer, based upon the Old Testament prophet Elijah, whom the Scriptures state rode a flaming chariot through heaven; this seemed a good enough approximation of the old thunder god with his fiery bolts. In the west, the Roman Catholic Church offered St. Michael the Archangel, who, as a commander of heavenly armies and vanquisher of the Devil, was also a fitting replacement for Perun. It is also possible that on a local level Perun was replaced with St. Vitus, where this saint did not, due to similarities in names, replace another important Slavic god, Svantevit; however, it is also possible that already in pagan times, the worship of Perun was challenged by a growing cult of Svantevit. On some levels of folklore and popular Christianity, some of Perun's characteristics were passed on to the Christian God himself.