Who is Blue Duck from Lonesome Dove and what is their importance?

Blue Duck is a throwback from more dangerous times, Blue Duck is one of the Indians that Call and Gus didn't manage to hang or eliminate while they were cleaning up the country and making it safe. Blue Duck is a large and frightening man who has no morals or scruples. Happy to steal, rape, and pillage, he commands a rag tag group of Indians that know the back country well. He lives for the opportunity to kill Gus and Woodrow, and steals Lorena in the hopes that either or both will come for her and give him the opportunity. He steals Lorena right out of her camp, and passes her around the boys until she loses the will to live.