Who is Scyld? Where does he come from? Where does he go? What does he do?

Scyld (Shild in some versions) is the father of Beo.  Beo was Hrothgar's great-grandfather and Healfdane's grandfather.  Scyld was also, like his descendants, a Danish king, but he is the first in this family line of kings.  He is mythological in origin having some ties to Scandanavian mythology.  Some scholars have suggested that his presence has agricultural or relgious meaning.  According to the story, he traveled alone to the land of the Danes, rose from one who beat people into submission to one who was honored.  He was a brave king who ruled lands all around him for a very long time.  When he died, according to the story, his body was put in a burial ship that waited in the harbor.  The ship was loaded with treasure to accompany the dead Scyld and the ship was set sail to go wherever the wind would take it.  This was a highly honored treatment of the dead and reserved only for a very select few.  Most of this is explained in the opening 53 lines of the poem.