(), or (Finnish for 'male grandparent', 'grandfather', 'old man'), parallel to Uku in Estonian mythology, is the god of the sky, weather, harvest, and thunder in Finnish mythology.
, the Finnish word for thunder, is the diminutive form of the name . believes that , another Finnic sky god, is the origin of , but that as experienced very significant, although far from total, influence from the Indo-European sky god especially in the form of Thor. Some believe that 's original name was Baltic Perkūnas.
is held the most significant god of Finnish mythology, although it is disputed by scholars whether this is accountable to later Christian influence. In the folk poems and prayers he is also given the epithet ('Supreme God'), probably in reference to his status as the most highly regarded god and on the other hand his traditional domain in the heavens. Other names for include (, 'long'), (, 'father'), (, archaic form of the above, modern meaning 'great', 'big' or 'large'). Although portrayed active in myth, when appealed to makes all his appearances in legend solely by natural phenomena. According to , the name Ukko was sometimes used as a common noun or generalised epithet for multiple deities instead of denoting a specific god.
Origins
It is likely that the figure of is mostly Indo-European, possibly Baltic, in origin. is held by researchers of religion to be parallel to Indo-European patriarchal sky deities, for example to Zeus and Jupiter of the Classical Greco-Roman pantheon, the Indian Hindu god Indra, the Balto-Slavic god Perun-Perkūnas and the Norse god Thor. , a Germanic loan and cognate of Thor, was possibly an alternate name for . is rarely encountered in Finnish mythology, and had been relegated to the mere role of deity of harvest and success.
It is possible that when took the position of the preceding sky god , 's destiny was to become a mortal smith-hero. Stories tell about vaulting the sky-dome. Whether was an earlier, assumably Finnic sky deity is regardless highly questionable. Some researchers hold and equivalent.
The Sami worshipped a similar deity, called Aijeke, probably as result of cultural cross-contamination or common origin. The god was equated with Horagalles.
Finnish folklore
possessed a weapon, often a hammer called (Ukko's hammer), sometimes also an axe () or a sword, by which he struck lightning (see thunderbolt). 's weapon was largely comparable to the Norse Mjölnir, and Iron Age emblematic pendants depicting hammers and axes similar or identical to Scandinavian specimens have been unearthed in Finland. Like Mjölnir, 's weapon has been linked by some to the of the Corded Ware culture.
Thunderbolts were sometimes called (bolt of Ukko) or (arrow of Ukko). It is possible that the Birch bark letter no. 292, written in a Baltic-Finnic language and unearthed in Novgorod, makes use of the metaphor, also referring to as doom-god according to one interpretation translated by Yuri Yeliseyev in modern English and interpreted in modern Finnish: God's arrow, ten [is] your name. This arrow is God's own. The Doom-God leads. The name was also used of Neolithic stone tools such as battle axes, which were employed as thunderstones to be buried at the corners of dwellings
Thunderstorms were sometimes interpreted as result of copulating with his wife . He also was believed to cause thunderstorms by driving his chariot through the skies.
A viper with a serrated line on its back was considered a symbol of thunder. Neolithic stone carvings have been found in Russian Karelia which have features of both snakes and lightning. It is, however, uncertain whether these are directly connected to the figure of . Evidence for worship of snakes is found among different cultures around the Baltic, including the Estonians and Finns.
There is evidence that the rowan tree was held sacred to . , a vaguely defined being has been hypothesised to be cognate to Germanic words for the rowan tree through .
The ladybird was also considered sacred to and called (Ukko's cow). The Finnish name of the great mullein (Verbascum thapsus) is (Ukko's fire flower), is also linked to worship of .
Festivals dedicated to Ukko
Before the advent of Christianity, the Midsummer festival in Finland, today known as after John the Baptist (), was held in honor of and called (Festival of Ukko). This tradition carried to the 19th century.