Hellen is an English-language (ie English, Australian, American, Canadian etc) variation of
Helen. I don't know when it was first used, but it was around 600th in popularity in the USA between 1910 and 1939 - in all other decades since 1900 it has been less than 1000th in popularity.
Click on the
Helen hyperlink for details on its meaning (unfortunately the meaning is uncertain but all the info is there).