Perkele

Perkele () is a swear word in Finnish that means "evil spirit" or a version of "god damn". It is popular, and is most likely the most known Finnish curse word in the world.
Origins.
The name is Indo-European. Perkwunos is the reconstructed name of the god of thunder. Other gods said to have the same origin include Perkūnas (Lithuania), Pērkons (Latvia), Percunis (Prussia), Piarun (Belarus), Peko or Pekolasõ (Estonia), Parjanya (India), Fairguneis (Gothic), and Perun or Piorun (Bosnia, Bulgaria, Croatia, the Czech Republic, Poland, Russia, Ukraine, Serbia, Slovakia and Slovenia).
Some researchers think "Perkele" is an original name of the thunder god Ukko, the chief god of the Finnish pagan pantheon. There are related words in other Finnic languages. In Estonian, "põrgu" means hell and in Karelian, "perkeleh" means an evil spirit.
Use.
It has been used as a curse as a cry for the god for strength. It still is a common curse word in colloquial Finnish. Finnish people use the word to be more serious and powerful than less powerful curses. When the Research Institute for the Languages of Finland held a contest to nominate the "most energizing" word in the Finnish language, one of the suggestions was Perkele because "it is the curse word that gave the most strength for the reconstruction of Finland after the wars."
Introduction of Christianity.
As Finland was Christianized, the old Finnish deities were said to be demons, so "Devil" was translated to "Perkele" for the Finnish translation of the Bible. Some later translations use "paholainen" (the evil one) instead.