Perkele

Perkele is a Finnish word meaning 'evil spirit' and a popular Finnish profanity, used similarly to the English phrase god damn, although it is considered much more profane. It is most likely the most internationally known Finnish curse word.

Etymology
The name is of Indo-European origin; Perkwunos is the reconstructed name of the god of thunder.

Some researchers consider Perkele to be an original name of the thunder god Ukko, the chief god of the Finnish pagan pantheon, but this view is not shared by all researchers. There are related words in other Finnic languages: in Estonian, põrgu means hell, in Karelian perkeleh means an evil spirit.

Influence of Christianity
As Finland was Christianized, the ancient pre-Christian deities came to be regarded as demons. This led to the use of "Perkele" as a translation for "Devil" in the Finnish translation of the Bible. Later, in other translations, the word was rendered as paholainen (the evil one).