Perkele is very old Finnish word meaning the beast or the devil (or even Satan) which is used alot when swearing... Pretty powerful word due strong R in the middle of word. There is no such powerful word in english or even german language.
Whatsoever almost every rocker visited in Finland can pronounce it :)

Pronounced with stress in first letter.

During the time I've spent in the US, no Finnish word has achieved such popularity and a high level of usage among my peers than perkele. It's connotations are sundry. The most direct English equivalent would in my opinion be god damn.

Interesting that perkele is used in the Finnish translations of the Old and New Testament to indicate the Devil although the word originates from Russian and in fact means demon, evil spirit.

In fact "Perkele" was the ruler of the ancient Baltic gods, often referred by Finns as Ukko Ylijumala. At the time of the Swedish crusades to Finland, Perkele was given the meaning of "Satan", perhaps to help the Swedes to replace the old nature religions with Christianity.