Wikipedia
Lempo
Lempo is a sort of fiend from Finnish folklore and mythology. Lempo is the god of love and fertility in Finnish mythology.
After Christianity came to Finland, the reputation of Lempo worsened: (s)he is portrayed in the folklore usually as erratic spirit, as love can be capricious, even dangerous, and it could even take control of a being and turn them to destruction.
The words "lempo" and "hiisi" are also used as very mild swear words in the Finnish language. "Piru" is a slightly stronger swear word. This too is work of Christians, they weren't originally bad words.