I am from West Virginia, a place that has Byrd's name all over it, and for very good reasons. He was a great asset to this whole country, but the people of West Virginia are particularly indebted to him. He served as an advocate for a part of the country that often gets ignored.
On top of that, he was often faced with disagreement. He spoke out against the War on Iraq at a time when most people would not and he never changed his position. He even wrote a very critical book against the president, during Bush's term. And, likely, throughout the later part of Byrd's term he often heard that he was too old to serve and that he was no longer capable.
I didn't go into to much detail, but I would recommend looking up more about him.