Much can be learned about the beliefs of our ancient Germanic ancestors by exploring the mythology and folklore of closely related peoples such as the Balts, Celts and Slavs. Much also can be learned from the Finns and Estonians who shared a common Nordic living space with Germanic and Indo-European peoples.
The similarities in their mythologies is due to cultural borrowing and also to a common inheritance once shared between the Aryans and Finno-Ugric peoples.
One particular example of a shared inheritance is how the northern Thunder God is viewed. In Finland one of the names of the Thunder God is Tuuri who is probably the same deity as the better known axe and hammer wielding Ukko. Ukko is derived from the Finnish word for thunder Ukkonen. In this way they followed the example of the Germanic peoples who named their deity from thunder; Thunor/Thunaer and the Celtic Thunder God Taranis whose name is derived from the Proto-Celtic word for thunder, *Toranos. So both Thunor, Taranis and Ukko are personifications of thunder.
Tuuri is rarely referred to in the mythology of the Finns and appears to have been relegated to a `minor` role as a God of the harvest, luck and success. In modern Finnish tuuri does mean `luck`. There is a village, Tuuri in Alavus, Western Finland which appears to have been named after Him. His name is cognate with the Estonian Taara who is likewise a Finno-Ugric Thunder deity. Furthermore Tuuri appears to be also cognate with the Irish Tuireann whose name again points to a Proto-Indo-European root for `thunder`. Also related to the Germanic Thor is Horagalles, the Sami Thunder God.
"There were significant cross-cultural exchanges between the Sami and the Swedes/Norwegians: the Sami thunder god, once named Tirmes, Turms, or Dierbmes, was to some extent repatterned after Thor. He gained the name Horagelles from `Thor karl` or `Thor kalle`[`Thor-fellow`]."[The Divine Thunderbolt. Missile of the Gods by J.T. Sibley, 2009]
The Finnish mythological epic The Kalevala which was recovered and published by Elias Lonnrot in 1849 is a collection of Finnish and Karelian oral myths and songs which Lonnrot collected and wrote down to form a cohesive epic. Similar activities of course occurred in 19th century Germany with the Grimm brothers who also committed to paper old German nursery rhymes, folklore and myths.
"Steady old Vainamoinen he hastened to ask: `Where did the fires go from there where did the sparks dash after Thor`s field edge-to the forest or to sea?"[Rune 47]
Ukko is equated with Perkele and it is believed by some scholars that this was Ukko`s original name. This is obviously related to the Proto-Indo-European *Perkunos or *Perkwunos.The similarity to the Lithuanian Perkunas and the Latvian Perkons is obvious. The Estonian version is Peko or Pekolaso. The Indo-European origins of Ukko and Tuuri thus established it is a reasonable strategy for us to examine Finnish and Estonian mythology for other traces of Indo-European concepts and in so doing we recover some of our own lost Aryan heritage.