Who is "Samuel" in the story of Saul, Samuel, and the Medium? In 1st Samuel 28, Saul gets the witch of Endor to summon Samuel back from the dead.  Is this really Samuel or some demon impersonating Samuel?

If it is the real Samuel here, how does this woman have the power to pull Samuel from Abraham's bosom (re: the story of Lazarus) back into this world?
This is a very tricky set of verses to interpret. Some think it is the Devil taunting Saul, but others think God used the very vices that Saul sought in his guilt to reprove him and prophecy against him.

I prefer the second option, that is this apparition is not of the Devil, but quite contrary to the woman’s satanic powers God used the occasion to overwhelm Saul so that wherever Saul turned God’s frown would follow him as a horrid curse.

To wonder whether Samuel appeared objectively or by a vision, I would lean towards merely a vision because his soul appears to have come out of the earth in the vision.  Naturally there was a belief that holy disembodied souls lived in heaven and if the vision was meant to be assumed as objective, the real soul of Samuel would probably have come from the sky down to the earth as that would have been more in keeping with how Enoch, Elijah and Jesus left the earth.



Addition

Contrary to what one might think today there were some Jewish beliefs before Christ of the soul going to paradise, or the Bosom of Abraham. The Sadducess did not probably hold this view but Jesus mentioning the Bosom of Abraham was probably in line with some of the views held in the traditios of the Pharisees.  In any case the famous Jewish historian says:


  the carrying up of the soul of the righteous by Angels is certainly in accordance with Jewish teaching, though stripped of all legendary details, such as about the number and the greetings of the Angels. (Alfred Edersheim Life and Times of Jesus, P858)


As another sample, in the Hebrew writings of the Maccabess we have similar ideas in accordance with the jokes that people have today about Peter meeting us at the pearly gates:


  For if we so die, Abraham and Isaac and Jacob will welcome us, and all the fathers will praise us. (4 Maccabees 13:17)


Although it may be difficult to prove when the Hebrews started to beleive in paradise as recording in ancient rabbinic literature, there seems to be logical grounds for assuming very early on. It is plausable that before Isaac was born Abraham had faith that his soul would go to his ancestors when his body was burried. His belief that God could raise Isaac from the dead is described in the New Tetament as the reason why he was willing to kill him.


  You, however, will go to your ancestors in peace and be buried at a good old age. (NIV Genesis 15:15)