The Dread Pirate Roberts is a character in the book (and movie), The Princess Bride.
The idea of the Dread Pirate Roberts always intrigued me. Passing a name on to someone else is the perfect way to build a truly larger than life character. But unfortunately that is much more difficult to do in this modern world of photographs, fingerprints, and retinal scans. But I have read a few science fiction stories that put the idea to good use.
The Dread Pirate Roberts has been a plague upon the lands of Florin and Guilder for over twenty years. But the original Dread Pirate Roberts soon grew tired of the pirate lifestyle and passed the title onto a man named Cummerbun. From there the title went to a man named Ryan.
Ryan met Westley when the Dread Pirate's ship attacked the ship that Westley was a passenger on. Ryan spared Westley's life, and they eventually became friends. Eventually the time came for Ryan to retire. He decided to pass the name onto Westley. They took on a new crew and Ryan stayed on for a while, calling Westley "Dread Pirate Roberts", in order to convince the new crew. The story suggests that Westley may have passed the title onto Inigo Montoya, but we will never get to know for sure.
Now the whole idea of Westley being the Dread Pirate Roberts is fascinating, but it doesn't seem to go along with his character. I first realized this when I was attempting to assign good old fashioned AD&D alignments to the characters in The Princess Bride. All the characters were fairly straightforward, except Westley. You see the Dread Pirate Roberts never left any survivors, that is said in the story more than once. So how could Westley be the Dread Pirate Roberts, while still upholding the code of conduct he displayed in the rest of the film? He said it himself, "Once word gets out that a pirate has gone soft, then its nothing but work, work, work."
Westley seems to spare almost everyone's life in this movie. He didn't kill Inigo Montoya or Fezzik when he could have done so easily. He even spared Prince Humperdink, who as an evil monarch should have definitely been disposed of. I just have to wonder how could this "sportmanlike" man live up to the name "Dread Pirate Roberts" for even a few months, without word getting out that he had "gone soft" (and for that matter why didn't he come for Buttercup sooner). The only solution I was able to come up with was that Westley had a very well developed dark side to his personality, and a lot of that "Dread Pirate/Man in Black" act that he was putting on was not so much an act, but was him acting out that part of his personality.