Wikipedia
[[Image:Ukkosjumalan aseet4.png|thumb|200px|Pre-Christian pendants associated with gods of thunder.
A) "Finnish type",
B) "Swedish type",
C) "Wolf's cross".
]]
Ukko, or Äijä or Äijö ( Finnish: male grandparent, grandfather, old man), parallel in Estonian mythology to Uku, is the god of the sky, weather, harvest and thunder in Finnish mythology. The Finnish word for thunder, Ukkonen, is the diminutive form of the name Ukko. Some researchers believe that Ilmarinen, another Finnic sky god, is the origin of Ukko, while some others believe that Ukko's original name was Baltic Perkele. Ukko 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 Ylijumala (English: Overgod), 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 Ukko include Pitkänen (pitkä, "long"), Isäinen (isä, "father"), Isoinen (iso, archaic form of the above, modern meaning "great"). Although portrayed active in myth, Ukko makes all his appearances in legend solely by natural phenomena when appealed to.
According to Haavio, the name Ukko was sometimes used as a common noun or generalised epithet for multiple deities instead of denoting a specific god.