I refer to Sauron, I just didn't want to write him as person because it might be little bit confusing, since it was him personally who captured Beren and Felagund; and in the case of Frodo and Thráin he was not personally involved in the capture.
Okay, what do these characters have in common:
Aragorn
Frodo
Gollum
the Lord of the Ringwraith
Sam