According to Oxford Online Dictionary lone wolf means the following:
A person who prefers to act alone: he’s a lone wolf; that’s what made him a successful foreign correspondent.
After the mass shootout (massacre) in San Berdadino in the US, I hear this compound noun very often. I believe the US media and President Obama call them lone wolf actors because they doubt the couple received any order from ISIS for the attack and acted alone.
According to Etymology Online Dictionary, the word wolf had a sexual connotation when it was first used to describe people:
Wolves as a symbol of lust are ancient, such as Roman slang lupa "whore," literally "she-wolf" (preserved in Spanish loba, Italian lupa, French louve). The equation of "wolf" and "prostitute, sexually voracious female" persisted into 12c., but by Elizabethan times wolves had become primarily symbolic of male lust. The specific use of wolf for "sexually aggressive male" first recorded 1847; wolf-whistle attested by 1945, American English, at first associated with sailors. The image of a wolf in sheep's skin is attested from c. 1400. See here for a discussion of "wolf" in Indo-European history. The wolf-spider so called for prowling and leaping on its prey rather than waiting in a web.
What is the etymology of the compound noun lone wolf? It doesn't seem to have started to mean what it means now as it doesn't have any sexual connotation at all. Some change might have happened in the meaning of the noun wolf (I suspect).
Does lone wolf have something to do with the word werewolf which means:
(In folklore) a person who changes for periods of time into a wolf, typically when there is a full moon.